Chronic Non-cancer Pain In Adults Research Articles

Ketamine for Chronic Non-Cancer Pain: A 2023 Update

What Is the Issue?
 
 Doctors use ketamine to induce loss of consciousness as general anesthesia during surgery. At low doses that do not produce dissociation, practitioners use ketamine to relieve acute or chronic pain.
 The previous CADTH report published in 2020 found that IV ketamine, compared to placebo, could only provide short-term pain relief in patients with chronic non-cancer pain, with increased risks of nausea, vomiting, and psychomimetic effects. The included guidelines did not provide definitive recommendations due to insufficient evidence.
 Decision-makers want to know if there is any new evidence to support the use of ketamine for treating of chronic non-cancer pain in adults.
 
 What Did We Do?
 
 To inform decisions about the use of ketamine for treating of chronic non-cancer pain, CADTH sought to update the previous report by identifying and summarizing literature comparing the clinical effectiveness and cost-effectiveness of ketamine with placebo or other pharmacological therapies for chronic non-cancer pain. We also attempted to identify evidence-based recommendations from most recent guidelines for the use of ketamine for chronic non-cancer pain.
 A research information specialist conducted a literature search of the peer-reviewed and grey literature with a search strategy focused on ketamine, chronic non-cancer pain, and adults. The search was limited to English-language documents published since 2020 up to November 06, 2023. One reviewer screened articles for inclusion based on predefined criteria, critically appraised the included studies, and narratively summarized the findings.
 
 What Did We Find?
 
 We found 3 SRs and 1 randomized controlled trial on the use of ketamine for the treatment of patients with neuropathic pain, complex regional pain syndrome, fibromyalgia, and other chronic pain conditions. Collective evidence from the included studies suggests that ketamine treatment was associated with short-term pain reduction in patients with chronic non-cancer pain. However, the long-term efficacy of ketamine in pain relief remains unclear.
 Adverse events (AEs) associated with ketamine treatment were with psychedelic effects, discomfort, dizziness, fatigue, headache, and nausea; all of those events appeared to be short-lasting.
 There were mixed results regarding the effect of ketamine on quality of life and functional improvement.
 We did not find any studies on the cost-effectiveness of ketamine or new evidence-based guidelines on the use of ketamine for treating chronic non-cancer pain.
 
 What Does It Mean?
 
 The findings in this review are consistent with the previous CADTH report published in 2020.
 Well-controlled studies with larger populations and longer follow-ups are needed to determine the optimal treatment protocol of ketamine for each specific type of chronic pain.
 Given that ketamine is a dissociative drug that could be associated with the development of a substance use disorder, decision-makers may wish to consider the use of ketamine for long-term treatment of chronic non-cancer pain. The long-term effects and dangers of ketamine remain to be determined.

High-dose opioids for chronic non-cancer pain: an overview of Cochrane Reviews.

This overview was originally published in 2017, and is being updated in 2022. Chronic pain is typically described as pain on most days for at least three months. Chronic non-cancer pain (CNCP) is any chronic pain that is not due to a malignancy. Chronic non-cancer pain in adults is a common and complex clinical issue, for which opioids are prescribed by some physicians for pain management. There are concerns that the use of high doses of opioids for CNCP lacks evidence of effectiveness, and may increase the risk of adverse events. To describe the evidence from Cochrane Reviews and overviews regarding the efficacy and safety of high-dose opioids (defined as 200 mg morphine equivalent or more per day) for CNCP. We identified Cochrane Reviews and overviews by searching the Cochrane Database of Systematic Reviews in The Cochrane Library. The date of the last search was 21 July 2022. Two overview authors independently assessed the search results. We planned to analyse data on any opioid agent used at a high dose for two weeks or more for the treatment of CNCP in adults. We did not identify any reviews or overviews that met the inclusion criteria. The excluded reviews largely reflected low doses or titrated doses, where all doses were analysed as a single group; we were unable to extract any data for high-dose use only. There is a critical lack of high-quality evidence, in the form of Cochrane Reviews, about how well high-dose opioids work for the management of CNCP in adults, and regarding the presence and severity of adverse events. No evidence-based argument can be made on the use of high-dose opioids, i.e. 200 mg morphine equivalent or more daily, in clinical practice. Considering that high-dose opioids have been, and are still being used in clinical practice to treat CNCP, knowing about the efficacy and safety of these higher doses is imperative.

Epidemiological Factors Associated with Prescription of Opioids for Chronic Non-Cancer Pain in Adults: A Country-Wide, Registry-Based Study in Denmark Spans 2004-2018.

Denmark has a high consumption of prescribed opioids, and many citizens with chronic non-cancer pain (CNCP). Therefore, we aimed to characterize and assess epidemiological risk factors associated with long-term non-cancer opioid use among Danish citizens. We conducted a longitudinal, retrospective, observational, register-based study using nationwide databases containing essential medical, healthcare, and socio-economic information. Statistical analysis, including backward stepwise logistic regression analysis, was used to explain long-term opioid use by individuals filling at least one prescription for an opioid product N02AA01-N02AX06 during 01/01/2004-31/12/2017, follow-up until the end of 2018. The analyzed cohort contained N=1,683,713 non-cancer opioid users, of which 979,666 were classified with CNCP diagnosis using ICD-10 codes. Long-term opioid use was predicted by a mean of 1,583.30 and a median of 300 oral morphine equivalent mg (OMEQ) per day during the first year, together with divorced, age group 40-53 years, retirement, receiving social welfare or unemployment ≥6 months. In addition, living in Northern Jutland, co-medications such as beta-blockers, anti-diabetics, anti-rheumatics, and minor surgery ≤90 days before inclusion. Protective variables were an education level of secondary school or higher, children living at home, household income of middle or highest tertile, opioid doses in either the 2nd or 3rd quartile OMEQ, male, the oldest age group, living in the Capital Region or Zealand, co-medication lipid-lowering, one comorbidity, heart failure, surgeries ≤90 days before the index: lips/teeth/jaw/mouth/throat, heart/vessels, elbow/forearm, hip/thigh, knee/lower leg/ankle/foot. Long-term opioid users differ epidemiologically from those using opioids for a shorter period. The study findings are essential for future recommendations revision in Denmark and comparable countries.

Nutritional aspects in chronic non-cancer pain: A systematic review

ObjectivesChronic pain (CP) is an unpleasant emotional and sensory experience that can be accompanied by tissue damage that persists for more than 3 months. Recent studies show that certain nutritional strategies can help to improve pain, so this study is aimed to systematically review scientific evidence to understand and map the effect of the use of nutritional strategies on the presence or intensity of chronic non-cancer pain (CNCP) and the association of these nutritional aspects with the presence or intensity of CNCP.Study designA systematic review.MethodsTwo independent researchers searched for randomized clinical trials (RCTs) and observational studies that explored the relationship between nutrition and CNCP in adults from 2010 to 2020 in PubMed, Web of Science, Scopus, and Cochrane Library databases. A total of 24 studies were included, of which 20 were RCTs and 4 were observational studies. They are classified into the administration of nutritional supplements, dietary modification, and incorporation of food.ResultsOf these studies, those that have a significant effect on pain are dietary modification and the use of nutritional supplements. On the other hand, the main results from the few observational studies included in this review point to the existence of an association relationship between less pain and a ketogenic or hypocaloric diet or adherence to the Mediterranean diet.ConclusionDietary modification seems to be one plausible therapeutic option to improve and relieve CNCP. However, more research is needed in this regard to obtain better conclusions.Systematic Review Registration[www.crd.york.ac.uk/prospero], identifier [CRD42021226431].

Magnesium for the Management of Chronic Noncancer Pain in Adults: Protocol for a Systematic Review.

BackgroundChronic pain is a highly prevalent and complex health problem that is associated with a severe symptom burden, as well as substantial economic and social impact. Many patients with chronic pain still suffer from unrelieved or undertreated pain due to the incomplete efficacy and dose-limiting adverse effects of current therapies. Long-term and high-dose opioid use has considerably increased in the past 20 years despite limited evidence supporting its effectiveness in several chronic pain conditions, and serious concerns have emerged regarding adverse effects and potential misuse. Until recently, the steady increase in opioid prescribing rates has been associated with rising opioid-related mortality and other serious problems, emphasizing the need for better nonopioid therapies. Emerging evidence supports the safe use of magnesium in controlling chronic pain, but its overall efficacy and safety is still unclear.ObjectiveThis paper aims to assess the efficacy and safety of magnesium compared with a placebo for the treatment of chronic noncancer pain.MethodsWe will conduct a detailed search on Cochrane Central Register of Controlled Trials, MEDLINE, and EMBASE from their inception until the date the searches are run to identify relevant randomized controlled trials. The reference lists of retrieved studies as well as Web-based trial registries will also be searched. We will include randomized double-blind trials comparing magnesium (at any dose, frequency, or route of administration) with placebo using participant-reported pain assessment. Two reviewers will independently evaluate studies for eligibility, extract data, and assess trial quality and potential bias. Risk of bias will be assessed using criteria outlined in the Cochrane Handbook for Systematic Review of Interventions. Primary outcomes for this review will include any validated measure of pain intensity or pain relief. Dichotomous data will be used to calculate the risk ratio and number needed to treat or harm. The quality of evidence will be assessed using the Grading of Recommendations Assessment, Development and Evaluation approach.ResultsThis protocol is grant-funded and has undergone a peer-review process through the Queen’s University Department of Anesthesiology and Perioperative Medicine Vandewater Endowed Studentship. This project is also supported, in part, by the Chronic Pain Network of the Canadian Institutes of Health Research Strategy for Patient-Oriented Research. The electronic database search strategies are currently being developed and modified. The entire review is expected to be completed by January 1, 2019.ConclusionsThe completion of this review is expected to identify available high-quality evidence describing the efficacy and safety of magnesium for the treatment of chronic noncancer pain.International Registered Report Identifier (IRRID)PRR1-10.2196/11654

Interventions for the reduction of prescribed opioid use in chronic non-cancer pain.

This is the first update of the original Cochrane Review published in 2013. The conclusions of this review have not changed from the 2013 publication. People with chronic non-cancer pain who are prescribed and are taking opioids can have a history of long-term, high-dose opioid use without effective pain relief. In those without good pain relief, reduction of prescribed opioid dose may be the desired and shared goal of both patient and clinician. Simple, unsupervised reduction of opioid use is clinically challenging, and very difficult to achieve and maintain. To investigate the effectiveness of different methods designed to achieve reduction or cessation of prescribed opioid use for the management of chronic non-cancer pain in adults compared to controls. For this update we searched CENTRAL, MEDLINE, and Embase in January 2017, as well as bibliographies and citation searches of included studies. We also searched one trial registry for ongoing trials. Included studies had to be randomised controlled trials comparing opioid users receiving an intervention with a control group receiving treatment as usual, active control, or placebo. The aim of the study had to include a treatment goal of dose reduction or cessation of opioid medication. Two review authors independently extracted data and assessed risk of bias. We sought data relating to prescribed opioid use, adverse events of opioid reduction, pain, and psychological and physical function. We planned to assess the certainty of the evidence using the GRADE approach, however, due to the heterogeneity of studies, we were unable to combine outcomes in a meta-analysis and therefore we did not assess the evidence with GRADE. Three studies are new to this update, resulting in five included studies in total (278 participants). Participants were primarily women (mean age 49.63 years, SD = 11.74) with different chronic pain conditions. We judged the studies too heterogeneous to pool data in a meta-analysis, so we have summarised the results from each study qualitatively. The studies included acupuncture, mindfulness, and cognitive behavioral therapy interventions aimed at reducing opioid consumption, misuse of opioids, or maintenance of chronic pain management treatments. We found mixed results from the studies. Three of the five studies reported opioid consumption at post-treatment and follow-up. Two studies that delivered 'Mindfulness-Oriented Recovery Enhancement' or 'Therapeutic Interactive Voice Response' found a significant difference between groups at post-treatment and follow-up in opioid consumption. The remaining study found reduction in opioid consumption in both treatment and control groups, and between-group differences were not significant. Three studies reported adverse events related to the study and two studies did not have study-related adverse events. We also found mixed findings for pain intensity and physical functioning. The interventions did not show between-group differences for psychological functioning across all studies. Overall, the risk of bias was mixed across studies. All studies included sample sizes of fewer than 100 and so we judged all studies as high risk of bias for that category. There is no evidence for the efficacy or safety of methods for reducing prescribed opioid use in chronic pain. There is a small number of randomised controlled trials investigating opioid reduction, which means our conclusions are limited regarding the benefit of psychological, pharmacological, or other types of interventions for people with chronic pain trying to reduce their opioid consumption. The findings to date are mixed: there were reductions in opioid consumption after intervention, and often in control groups too.

High-dose opioids for chronic non-cancer pain: an overview of Cochrane Reviews.

Chronic pain is typically described as pain on most days for at least three months. Chronic non-cancer pain (CNCP) is any chronic pain that is not due to a malignancy. Chronic non-cancer pain in adults is a common and complex clinical issue where opioids are routinely used for pain management. There are concerns that the use of high doses of opioids for chronic non-cancer pain lacks evidence of effectiveness and may increase the risk of adverse events. To describe the evidence from Cochrane Reviews and Overviews regarding the efficacy and safety of high-dose opioids (here defined as 200 mg morphine equivalent or more per day) for chronic non-cancer pain. We identified Cochrane Reviews and Overviews through a search of the Cochrane Database of Systematic Reviews (The Cochrane Library). The date of the last search was 18 April 2017. Two review authors independently assessed the search results. We planned to analyse data on any opioid agent used at high dose for two weeks or more for the treatment of chronic non-cancer pain in adults. We did not identify any reviews or overviews meeting the inclusion criteria. The excluded reviews largely reflected low doses or titrated doses where all doses were analysed as a single group; no data for high dose only could be extracted. There is a critical lack of high-quality evidence regarding how well high-dose opioids work for the management of chronic non-cancer pain in adults, and regarding the presence and severity of adverse events. No evidence-based argument can be made on the use of high-dose opioids, i.e. 200 mg morphine equivalent or more daily, in clinical practice. Trials typically used doses below our cut-off; we need to know the efficacy and harm of higher doses, which are often used in clinical practice.

Adverse events associated with medium- and long-term use of opioids for chronic non-cancer pain: an overview of Cochrane Reviews.

Chronic pain is common and can be challenging to manage. Despite increased utilisation of opioids, the safety and efficacy of long-term use of these compounds for chronic non-cancer pain (CNCP) remains controversial. This overview of Cochrane Reviews complements the overview entitled 'High-dose opioids for chronic non-cancer pain: an overview of Cochrane Reviews'. To provide an overview of the occurrence and nature of adverse events associated with any opioid agent (any dose, frequency, or route of administration) used on a medium- or long-term basis for the treatment of CNCP in adults. We searched the Cochrane Database of Systematic Reviews (the Cochrane Library) Issue 3, 2017 on 8 March 2017 to identify all Cochrane Reviews of studies of medium- or long-term opioid use (2 weeks or more) for CNCP in adults aged 18 and over. We assessed the quality of the reviews using the AMSTAR criteria (Assessing the Methodological Quality of Systematic Reviews) as adapted for Cochrane Overviews. We assessed the quality of the evidence for the outcomes using the GRADE framework. We included a total of 16 reviews in our overview, of which 14 presented unique quantitative data. These 14 Cochrane Reviews investigated 14 different opioid agents that were administered for time periods of two weeks or longer. The longest study was 13 months in duration, with most in the 6- to 16-week range. The quality of the included reviews was high using AMSTAR criteria, with 11 reviews meeting all 10 criteria, and 5 of the reviews meeting 9 out of 10, not scoring a point for either duplicate study selection and data extraction, or searching for articles irrespective of language and publication type. The quality of the evidence for the generic adverse event outcomes according to GRADE ranged from very low to moderate, with risk of bias and imprecision being identified for the following generic adverse event outcomes: any adverse event, any serious adverse event, and withdrawals due to adverse events. A GRADE assessment of the quality of the evidence for specific adverse events led to a downgrading to very low- to moderate-quality evidence due to risk of bias, indirectness, and imprecision.We calculated the equivalent milligrams of morphine per 24 hours for each opioid studied (buprenorphine, codeine, dextropropoxyphene, dihydrocodeine, fentanyl, hydromorphone, levorphanol, methadone, morphine, oxycodone, oxymorphone, tapentadol, tilidine, and tramadol). In the 14 Cochrane Reviews providing unique quantitative data, there were 61 studies with a total of 18,679 randomised participants; 12 of these studies had a cross-over design with two to four arms and a total of 796 participants. Based on the 14 selected Cochrane Reviews, there was a significantly increased risk of experiencing any adverse event with opioids compared to placebo (risk ratio (RR) 1.42, 95% confidence interval (CI) 1.22 to 1.66) as well as with opioids compared to a non-opioid active pharmacological comparator, with a similar risk ratio (RR 1.21, 95% CI 1.10 to 1.33). There was also a significantly increased risk of experiencing a serious adverse event with opioids compared to placebo (RR 2.75, 95% CI 2.06 to 3.67). Furthermore, we found significantly increased risk ratios with opioids compared to placebo for a number of specific adverse events: constipation, dizziness, drowsiness, fatigue, hot flushes, increased sweating, nausea, pruritus, and vomiting.There was no data on any of the following prespecified adverse events of interest in any of the included reviews in this overview of Cochrane Reviews: addiction, cognitive dysfunction, depressive symptoms or mood disturbances, hypogonadism or other endocrine dysfunction, respiratory depression, sexual dysfunction, and sleep apnoea or sleep-disordered breathing. We found no data for adverse events analysed by sex or ethnicity. A number of adverse events, including serious adverse events, are associated with the medium- and long-term use of opioids for CNCP. The absolute event rate for any adverse event with opioids in trials using a placebo as comparison was 78%, with an absolute event rate of 7.5% for any serious adverse event. Based on the adverse events identified, clinically relevant benefit would need to be clearly demonstrated before long-term use could be considered in people with CNCP in clinical practice. A number of adverse events that we would have expected to occur with opioid use were not reported in the included Cochrane Reviews. Going forward, we recommend more rigorous identification and reporting of all adverse events in randomised controlled trials and systematic reviews on opioid therapy. The absence of data for many adverse events represents a serious limitation of the evidence on opioids. We also recommend extending study follow-up, as a latency of onset may exist for some adverse events.

Methadone for neuropathic pain in adults.

This review replaces an earlier review, "Methadone for chronic non-cancer pain in adults". This review serves to update the original and includes only studies of neuropathic pain. Methadone belongs to a class of analgesics known as opioids, that are considered the cornerstone of therapy for moderate-to-severe postsurgical pain and pain due to life-threatening illnesses; however, their use in neuropathic pain is controversial. Methadone has many characteristics that differentiate it from other opioids, which suggests that it may have a different efficacy and safety profile. To assess the analgesic efficacy and adverse events of methadone for chronic neuropathic pain in adults. We searched the following databases: CENTRAL (CRSO), MEDLINE (Ovid), and Embase (Ovid), and two clinical trial registries. We also searched the reference lists of retrieved articles. The date of the most recent search was 30 November 2016. We included randomised, double-blind studies of two weeks' duration or longer, comparing methadone (in any dose, administered by any route, and in any formulation) with placebo or another active treatment in chronic neuropathic pain. We used standard methodological procedures expected by Cochrane. Two review authors independently considered trials for inclusion in the review, assessed risk of bias, and extracted data. There were insufficient data to perform pooled analyses. We assessed the overall quality of the evidence for each outcome using GRADE and created a 'Summary of findings' table. We included three studies, involving 105 participants. All were cross-over studies, one involving 19 participants with diverse neuropathic pain syndromes, the other two involving 86 participants with postherpetic neuralgia. Study phases ranged from 20 days to approximately eight weeks. All administered methadone orally, in doses ranging from 10 mg to 80 mg daily. Comparators were primarily placebo, but one study also included morphine and tricyclic antidepressants.The included studies had several limitations related to risk of bias, particularly incomplete reporting, selective outcome reporting, and small sample sizes.There were very limited data for our primary outcomes of participants with at least 30% or at least 50% pain relief. Two studies reported that 11/29 participants receiving methadone achieved 30% pain relief versus 7/29 participants receiving placebo. Only one study presented data in a manner that allowed us to calculate the number of participants with at least 50% pain relief. None of the 19 participants achieved a 50% reduction in pain intensity, either when receiving methadone or when receiving placebo. No study provided data for our other primary outcomes of Patient Global Impression of Change scale (PGIC) much or very much improved (equivalent to at least 30% pain relief) and PGIC very much improved (equivalent to at least 50% pain relief).For secondary efficacy outcomes, one study reported maximum and mean pain intensity and pain relief, and reported statistically significant improvements versus placebo for all outcomes with 20 mg daily doses of methadone, but not with 10 mg daily doses. The second study reported differences in pain reduction between methadone (n = 26) and morphine (n = 38) and found morphine to be statistically superior. The third study reported the number of responders (variously defined) for several pain and functional outcomes and found methadone to be statistically superior to placebo for the outcomes of categorical pain intensity and evoked pain. In the two studies that reported data, 0/29 participants withdrew due to lack of efficacy, whereas 4/29 participants withdrew due to adverse events while taking methadone versus 3/29 while taking placebo.One study reported incidences for several individual adverse events, but found a statistically significant increased incidence for methadone over placebo for only one event, dizziness. The other studies did not report data in a manner that enabled us to analyze adverse events. There were no serious adverse events or deaths reported.We assessed the quality of the evidence as very low for all efficacy and safety outcomes using GRADE, primarily because of the heterogeneity of study designs and populations, short durations, cross-over methodology, and few participants and events. The three studies provide very limited, very low quality evidence of the efficacy and safety of methadone for chronic neuropathic pain, and there were too few data for pooled analysis of efficacy or harm, or to have confidence in the results of the individual studies. No conclusions can be made regarding differences in efficacy or safety between methadone and placebo, other opioids, or other treatments.

Trigger point manual therapy for the treatment of chronic non-cancer pain in adults

Reason for withdrawal from publication This protocol has been withdrawn as the full review did not meet Cochrane expectations of timeliness.

Opioid therapy for chronic non-cancer pain: guidelines for Hong Kong.

Opioids are increasingly used to control chronic non-cancer pain globally. International opioid guidelines have been issued in many different countries but a similar document is not generally available in Hong Kong. Chronic opioid therapy has a role in multidisciplinary management of chronic non-cancer pain despite insufficient evidence for its effectiveness and safety for long-term use. This document reviews the current literature to inform Hong Kong practitioners about the rational use of chronic opioid therapy in chronic non-cancer pain. It also aims to provide useful recommendations for the appropriate, effective, and safe use of such therapy in the management of chronic non-cancer pain in adults. Physicians should conduct a comprehensive biopsychosocial evaluation of patients prior to the commencement of opioid therapy. When opioid use is deemed appropriate, the patient should provide informed consent within an agreement that specifies treatment goals and expectations. A trial of opioid can be commenced and, provided there is progress towards treatment goals, then chronic therapy can be considered at a dose that minimises harm. Monitoring of effectiveness, safety, and drug misuse should be continued. Treatment should be stopped when opioids become ineffective, intolerable, or misused. The driving principles for opioid prescription in chronic pain management should be: start with a low dose, titrate slowly, and maintain within the shortest possible time.

Methadone for chronic non-cancer pain in adults

Methadone belongs to a class of analgesics known as opioids, that are considered the cornerstone of therapy for moderate-to-severe pain due to life-threatening illnesses; however, their use in chronic non-cancer pain (CNCP) is controversial. Methadone has many characteristics that differentiate it from other opioids, which suggests that it may have a different efficacy and safety profile. To assess the analgesic effectiveness and safety of methadone in the treatment of CNCP. We identified both randomized controlled trials (RCTs) and non-randomized studies of methadone use in chronic pain by searching the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library 2011, issue 11, MEDLINE (1950 to November 2011), and EMBASE (1980 to November 2011), together with reference lists of retrieved papers and reviews. We included RCTs with pain assessment as either the primary or secondary outcome. Quasi-randomized studies, cohorts and case-control trials were also considered for inclusion because we suspected that the beneficial and harmful effects of methadone in CNCP may not be adequately addressed in RCTs. Two review authors independently extracted efficacy and adverse event data and assessed risk of bias. We included two RCTs and one non-randomized study, involving a total of 181 participants. Both RCTs were cross-over studies, one involving 19 participants with diverse neuropathic pain syndromes, the other involving 76 participants with postherpetic neuralgia. Study phases were 20 days and approximately eight weeks, respectively. The non-randomized study retrospectively evaluated 86 outpatients over an average of 8.8 ± 6.3 months.One RCT reported average pain intensity and pain relief, and found statistically significant improvements versus placebo for both outcomes, with 10 mg and 20 mg daily doses of methadone. The second RCT reported differences in pain reduction between methadone and morphine and found morphine to be statistically superior. The non-randomized study found that in patients initially prescribed methadone it was effective in fewer participants than in those initially prescribed other long-acting opioids (28% versus 42%, 33% and 50% for morphine, oxycodone and transdermal fentanyl, respectively).One RCT compared incidences for several individual adverse events, but found a difference between methadone and placebo for only one event, dizziness (P = 0.041). The three studies provide very limited evidence of the efficacy of methadone for CNCP, and there were too few data for pooled analysis of efficacy or harm, or to have confidence in the results of the individual studies. No conclusions can be made regarding differences in efficacy or safety between methadone and placebo, other opioids, or other treatments.