Effects Of Caffeine Consumption Research Articles

Comparable Analysis of Acute Changes in Vascular Tone after Coffee versus Energy Drink Consumption.

Caffeinated beverages are popular throughout the world, especially due to their stimulating effects on body physiology. However, short- and long-term outcome studies have shown variable results on general health. In this pilot study, we exposed a cohort of 23 healthy individuals to 240 mg of caffeine either in the form of coffee or energy drinks and performed repetitive pulse wave analyses. This experimental approach was chosen to investigate the acute effects of caffeine consumption on vascular tone depending on the form of caffeine intake. Our data indicate that energy drinks, in contrast to coffee, might negatively impact systolic blood pressure and pulse wave velocity. This issue needs special attention in the light of cardiovascular health as the observed effects have been associated with an increased risk of cardiovascular events upon persistent exposure.

Effects of Caffeine Consumption on Autologous Full-Thickness Skin Graft Healing in an Animal Model.

Background There exists contradictory evidence that states both the beneficial and deleterious effects of caffeine on wound healing. The general population might unknowingly consume caffeine that negatively affects wound healing. The main objective of this study is to investigate the effect of daily caffeine consumption on wound healing, specifically full-thickness skin graft (FTSG). Methods Forty Sprague–Dawley rats were randomized into four groups of equal size: control-dose (CD), low-dose (LD), medium-dose (MD), and high-dose (HD) caffeine groups. After autologous FTSG, all subjects in the intervention group were given daily pure caffeine gavage. The FTSG was explanted 7 days posttransplant. The graft viability, secondary contraction, and adherence were evaluated macroscopically, while fibroblast and collagen deposition was analyzed microscopically with hematoxylin eosin stain. Results The least graft viability (72.8 ± 20.7%, clinical wound assessment scale [CWAS] 2.4), highest secondary contraction (11.4 ± 10.5%), and fibroblast count (331.8 ± 88.6 cells/5 high power fields) were observed in the MD group. More collagen synthesis was observed in subjects who consumed caffeine. The level of secondary contraction, fibroblast count as well as graft viability and collagen synthesis were positively correlated. Conclusions Daily consumption of caffeine impairs graft viability when given in medium dose and increases collagen synthesis, irrespective of dosage. This study was in experimental rats; the results are not directly translatable to humans.

The Neurophysiology of Caffeine as a Central Nervous System Stimulant and the Resultant Effects on Cognitive Function.

Caffeine is one of the world’s most consumed drugs. According to the Washington Post (2015), two billion cups of coffee are consumed per day worldwide. Caffeine is classified as a central nervous system (CNS) stimulant and an organic molecule called methylxanthine. Caffeine has three notable mechanisms of action on the CNS that produce a psychostimulant effect. These effects are responsible for the effect that caffeine has on cognitive function. The effects of caffeine consumption on cognitive function have been demonstrated across several studies involving humans and animals. With the immense number of people consuming caffeine around the world, it is of vital importance to study the effects that this drug has on people’s cognitive function. This literature review provides useful insights on this question through the analysis of caffeine’s effects on cognitive function, along with information on caffeine’s three modes of action. The findings of recent studies show mixed results regarding the effects of caffeine on mood, attention, processing speed, and memory. Current research suggests that if caffeine does have an effect on mood, the most significant changes may be anxiety. Studies did not support caffeine as having any significant effect on attention, but that it did play a role in enhancing processing speed. The majority of the studies reviewed suggest caffeine as having a significant positive effect on both short and long-term memory in adults and the elderly. Current findings warrant continued research on the association of caffeine and the resultant effects on cognitive function.

The Effects of Regular Versus Irregular Caffeine Consumption in Mental Performance

Caffeine is the most widely used psychoactive drug in the world and is a central nervous system stimulant that increases alertness and excitation. Regular consumption of caffeine can cause one to become dependent on the drug and this, in turn, can cause withdrawal to occur when regular caffeine consumption is disrupted [1]. A case study series (3 cases) addresses the way in which caffeine consumption by regular and irregular caffeine drinkers impacts cognitive performance. Three subjects, 2 regular caffeine drinkers and 1 irregular caffeine drinker, performed case studies to examine the effect of caffeine consumption on their reaction and choice reaction times. A Brain Gauge device and software were used to conduct these cognitive performance tasks. Across all 3 cases, choice reaction time decreased (i.e., task performance improved) after drinking coffee. In most cases, there was a decrease in the average reaction time (performance improvement) after caffeine consumption. The difference in mental performance between regular and irregular drinkers cannot be determined with the results of this case study series. Additional research and experiments with larger sample sizes are needed before making further conclusions about how caffeine consumption and disruption of caffeine consumption affects mental performance.

Interdisciplinary Collaborative Learning as an Alternate to In‐person Laboratory Experiences for Exercise Science and Biology Undergraduate Students

The COVID-19 pandemic caused major challenges to in-person undergraduate laboratory experiences, forcing instructors to find new methods for content delivery and skills development. A spring 2020 collaborative project examining maximal oxygen consumption, lactate threshold, and effects of caffeine consumption on maximal exercise performance paired Exercise Physiology students with Human Anatomy and Physiology (A&P) students to meet learning goals for both courses and to facilitate remote research skill development. The project replaced a hands-on A&P investigation that fulfills conceptual knowledge, data analysis, and communication learning goals and Exercise Science course-based undergraduate research experiences that meet conceptual knowledge and inquiry and analysis learning goals. 24 upper-level undergraduate Exercise Physiology students with VO2max and lactate threshold testing experience served as Consultants to upper-level undergraduate A&P students. A&P students (138 students; 9 laboratory sections) were divided into 31 groups of 4-5 students, with 1-3 groups assigned to each Consultant. Groups were intentionally structured to include a diversity of majors and GPAs. Students were provided with data collected in previous years. Consultants met with each group at least 3 times, serving as expert advisors to help A&P students: 1) understand VO2max and lactate threshold physiology, 2) understand VO2max and lactate threshold testing procedures, 3) develop a research question with appropriately-designed data comparisons and statistical tests, 4) analyze data from two conditions (caffeine and no caffeine), and 5) create appropriate figures, analyze results, and form conclusions based on data. The project successfully replaced a hands-on lab experience due to the Consultants’ prior experience conducting and analyzing data from maximal exercise tests, as well as developing research questions based on maximal exercise testing. Consultants provided A&P students with an additional resource for success and helped instructors manage their workload during the transition to emergency online instruction. A&P students indicated the project was generally successful, although they would have preferred in-person data collection experience and more direct supervision from instructors. Consultants indicated their previous experience with protocols and content was helpful, and teaching peers reinforced their understanding. Challenges included relative timing of instruction on fundamentals of exercise testing vs. data availability, scheduling conflicts, and the sudden move to remote learning. Interdepartmental collaborative projects that pair students with prior in-person data collection experience as Consultants for peers may provide a useful alternative to in-person labs because they reinforce Consultant understanding of procedures and data analysis, build peer understanding of procedures and data analysis, and manage instructor workload.

Effects of adolescent caffeine consumption on cocaine self-administration and reinstatement of cocaine seeking.

Caffeine consumption by children and adolescents has risen dramatically in recent years, yet the lasting effects of caffeine consumption during adolescence remain poorly understood. These experiments explore the effects of adolescent caffeine consumption on cocaine self-administration and seeking using a rodent model. Sprague-Dawley rats consumed caffeine for 28 days during the adolescent period. Following the caffeine consumption period, the caffeine solution was replaced with water for the remainder of the experiment. Age-matched control rats received water for the duration of the study. Behavioral testing in a cocaine self-administration procedure occurred during adulthood (postnatal days 62-82) to evaluate how adolescent caffeine exposure influenced the reinforcing properties of cocaine. Cocaine seeking was also tested during extinction training and reinstatement tests following cocaine self-administration. Adolescent caffeine consumption increased the acquisition of cocaine self-administration and increased performance on different schedules of reinforcement. Consumption of caffeine in adult rats did not produce similar enhancements in cocaine self-administration. Adolescent caffeine consumption also produced an upward shift in the U-shaped dose response curve on cocaine self-administration maintained on a within-session dose-response procedure. Adolescent caffeine consumption had no effect on cocaine seeking during extinction training or reinstatement of cocaine seeking by cues or cocaine. These findings suggest that caffeine consumption during adolescence may enhance the reinforcing properties of cocaine, leading to enhanced acquisition that may contribute to increased addiction vulnerability.

Caffeine increases parasympathetic reactivation without altering resting and exercise cardiac parasympathetic modulation: A balanced placebo design

The sympathicotonic effect of caffeine is strongly evidenced in the literature. However, the effects of caffeine or caffeine expectancy on the cardiac parasympathetic modulation remain obscure. Thus, the aim of this study was to investigate the effects of caffeine consumption and expectancy of caffeine consumption on the cardiac parasympathetic modulation under different stress conditions. Twenty-one physically active men (22.3 ± 2.9 years, 25.2 ± 2.7 kg/m2) consumed ∼3 mg/kg of caffeine received as caffeine, caffeine as placebo, placebo as placebo and placebo as caffeine. Parasympathetic modulation was assessed by heart rate variability (HRV-Poincaré SD1 index) at supine and orthostatic positions, during a submaximal exercise (HRV threshold-HRVT) and during each 60 seconds (s) within 300 s of post-exercise active recovery. A factorial ANOVA for repeated measures (p < 0.05) was used to assess the effect of caffeine, expectancy and resting time after caffeine intake on the HRV. No significant effect of caffeine or expectancy was observed on the SD1 value at supine or standing positions (p = 0.47–0.53; p = 0.57–0.31, respectively), despite an increase in this variable after resting periods in both positions (p < 0.001). During exercise, caffeine and expectancy do not alter the HRVT (p = 0.51–0.39). However, higher SD1 values were observed after caffeine administration from 60 to 300 s post-exercise recovery (p = 0.01–0.05) but not for the effects of expectancy (p = 0.19–0.94). We concluded that low doses of caffeine or expectancy do not alter the resting cardiac parasympathetic modulation or HRVT. However, caffeine, but not expectancy, increases parasympathetic reactivation after a submaximal exercise test in young men.

Effects of Caffeine Consumption on Endurance Exercise: A Systematic Review

Effects of Caffeine Consumption on Endurance Exercise: A Systematic Review

Effect of Caffeine on Attention and Alertness Measured in a Home-Setting, Using Web-Based Cognition Tests.

BackgroundThere is an increasing interest among nutritional researchers to perform lifestyle and nutritional intervention studies in a home setting instead of testing subjects in a clinical unit. The term used in other disciplines is ‘ecological validity’ stressing a realistic situation. This becomes more and more feasible because devices and self-tests that enable such studies are more commonly available. Here, we present such a study in which we reproduced the effect of caffeine on attention and alertness in an at-home setting.ObjectiveThe study was aimed to reproduce the effect of caffeine on attention and alertness using a Web-based study environment of subjects, at home, performing different Web-based cognition tests.MethodsThe study was designed as a randomized, placebo-controlled, double-blind, crossover study. Subjects were provided with coffee sachets (2 with and 2 without caffeine). They were also provided with a written instruction of the test days. Healthy volunteers consumed a cup of coffee after an overnight fast. Each intervention was repeated once. Before and 1 hour after coffee consumption subjects performed Web-based cognitive performance tests at home, which measured alertness and attention, established by 3 computerized tests provided by QuantifiedMind. Each test was performed for 5 minutes.ResultsWeb-based recruitment was fast and efficient. Within 2 weeks, 102 subjects applied, of whom 70 were eligible. Of the 66 subjects who started the study, 53 completed all 4 test sessions (80%), indicating that they were able to perform the do it yourself tests, at home, correctly. The Go-No Go cognition test performed at home showed the same significant improvement in reaction time with caffeine as found in controlled studies in a metabolic ward (P=.02). For coding and N-back the second block was performed approximately 10% faster. No effect was seen on correctness.ConclusionsThe study showed that the effects of caffeine consumption on a cognition test in an at-home setting revealed similar results as in a controlled setting. The Go-No Go test applied showed improved results after caffeine intake, similar as seen in clinical trials. This type of study is a fast, reliable, economical, and easy way to demonstrate effectiveness of a supplement and is rapidly becoming a viable alternative for the classical randomized control trial to evaluate life style and nutritional interventions.Trial RegistrationClinicaltrials.gov NCT02061982; https://clinicaltrials.gov/ct2/show/NCT02061982 (Archived by WebCite at https://clinicaltrials.gov/ct2/show/NCT02061982)

Effects of caffeine consumption in patients with chronic hepatitis C: A systematic review and meta-analysis

Increased caffeine consumption has been associated with a decreased risk of liver enzyme elevation, cirrhosis, and hepatocellular carcinoma. However, few studies have assessed these effects in patients with chronic hepatitis C; therefore, we conducted a systematic review and meta-analysis to investigate the impact of caffeine consumption in patients with chronic hepatitis C infection. We performed a comprehensive search of the databases of the Cochrane Central Register of Controlled Trials, MEDLINE, and EMBASE from inception through November 2015. The inclusion criterion was observational studies' assessment of the impact of caffeine consumption in adult patients with chronic hepatitis C. Eleven studies were included for full article review, and data was extracted from five observational studies for meta-analysis. The pooled odds ratio of advanced hepatic fibrosis in patients who had higher caffeine intake was 0.39 (95% confidence interval 0.21-0.72, P=0.003) compared with lower caffeine intake group. The statistical between-study heterogeneity was moderate with an I2 of 70%. Our meta-analysis demonstrated that caffeine intake is significantly associated with decreased odds of advanced hepatic fibrosis in patients with chronic hepatitis C. Future prospective studies assessing the optimal dose and preparation of caffeinated beverages for prevention of hepatic fibrosis are needed.

Preconception care: caffeine, smoking, alcohol, drugs and other environmental chemical/radiation exposure.

IntroductionAs providing health education, optimizing nutrition, and managing risk factors can be effective for ensuring a healthy outcome for women and her yet un-conceived baby, external influences play a significant role as well. Alcohol, smoking, caffeine use and other similar lifestyle factors, have now become an integral part of the daily life of most men and women, who use/misuse one or more of these harmful substances regularly despite knowledge of their detrimental effects. The adverse health outcomes of these voluntary and involuntary exposures are of even greater concern in women of child bearing age where the exposure has the potential of inflicting harm to two generations. This paper is examining the available literature for the possible effects of caffeine consumption, smoking, alcohol or exposure to chemicals may have on the maternal, newborn and child health (MNCH).MethodsA systematic review and meta-analysis of the evidence was conducted to ascertain the possible impact of preconception usage of caffeine, tobacco, alcohol and other illicit drugs; and exposure to environmental chemicals and radiant on MNCH outcomes. A comprehensive strategy was used to search electronic reference libraries, and both observational and clinical controlled trials were included. Cross-referencing and a separate search strategy for each preconception risk and intervention ensured wider study capture.ResultsHeavy maternal preconception caffeine intake of >300mg/d significantly increase the risk of a subsequent fetal loss by 31% (95% CI: 8-58%). On the other hand, preconception alcohol consumption leads to non-significant 30% increase in spontaneous abortion (RR 1.30; 95% CI: 0.85-1.97). Preconception counselling can lead to a significant decrease in the consumption of alcohol during the first trimester (OR 1.79; 95% CI: 1.08-2.97). Periconception smoking, on the other hand, was found to be associated with an almost 3 times increased risk of congenital heart defects (OR 2.80; 95% CI 1.76-4.47). While the review found limited evidence of preconception environmental exposure on maternal, newborn and child health outcomes, occupational exposure in female radiation workers before conception showed an increased impact in risk of early miscarriages.ConclusionIdentification of substance abuse and environmental history during preconception period provides an opportunity to assist women in reducing major health risks and identify key determinants of healthy pregnancy. Studies have shown that the aversion and prevention of exposure feasibility can play an important role in improving the health of women and their families, however, the results should be interpreted with great caution as there were few studies in each section. Therefore, there is a need for more rigorous studies to test the hypotheses.

Coffee Consumption Associated with Increased Mortality of Women with Breast Cancer.

There has been some speculation that caffeine consumption may affect breast cancer. Most case-control studies have not documented evidence of a caffeine-breast cancer incidence link; however, there has been very little analysis of the possible effects of caffeine consumption on breast cancer survival. We examined overall a 20-year survival of 96 women treated for breast cancer between 1990 and 1994. As part of their health history, these women were asked about coffee drinking. Fifty-three women drank one cup a day (79.2% survival), 22 women had two cups a day (72.7% survival), and 21 women drank three or more cups a day (42.9% survival). The effect of coffee consumption on survival was significant (p=0.006, the log rank test). To exclude the effects of lymph node involvement, age at diagnosis, and smoking history, Cox regression was performed. The effect of coffee was significant (p=0.001), independent of the effects of lymph node involvement (p=0.012) and age at diagnosis (p=0.014), and unrelated to a smoking history (p=0.721). Fatigued breast cancer survivors have an abnormal proinflammatory cytokine activity, an average of 5 years after diagnosis, as well as significant serum cortisol derangements compared to other survivors. One possible interpretation of our results suggests that there is an abnormal hypothalamic-pituitary-adrenal axis functioning in breast cancer patients with persistent fatigue, who might be using coffee to self-medicate. In other words, coffee consumption in the present study might be a surrogate marker for fatigue. Because of the paucity of data regarding caffeine intake, poor sleep, fatigue, and breast cancer survival, further studies could be worthwhile.

Effects of Caffeine Consumption by Women and Men on the Outcome of In Vitro Fertilization.

The objective of this study was to estimate the association between caffeine consumption and in vitro fertilization (IVF) outcomes. A total of 2474 couples were prospectively enrolled prior to undergoing their first cycle of IVF, contributing a total of 4716 IVF cycles. Discrete survival analysis adjusting for observed confounders was applied to quantify the relation between caffeine consumption and livebirth. Secondary outcomes of interest were oocyte retrieval, peak estradiol level, implantation rate, and fertilization rate. Overall, caffeine consumption by women was not significantly associated with livebirth (ptrend=0.74). Compared with women who do not drink caffeine, the likelihood of livebirth was not significantly different for women who drank low (>0-800 mg/week; odds ratio [OR]=1.00, 95% confidence interval [CI])=0.83-1.21), moderate (>800-1400 mg/week; OR=0.89, 95% CI=0.71-1.12), or high levels of caffeine (>1400 mg/week; OR=1.07, 95% CI=0.85-1.34). Greater caffeine intake by women was associated with a significantly lower peak estradiol level (ptrend=0.03), but was not associated with the number of oocytes retrieved (ptrend=0.75), fertilization rate (ptrend=0.10), or implantation rate (ptrend=0.23). There was no significant association between caffeine intake by men and livebirth (ptrend=0.27), fertilization (ptrend=0.72), or implantation (ptrend=0.24). The individual effects of consumption of coffee, tea, or soda by women or men were not related to livebirth. Caffeine consumption by women or men was not associated with IVF outcomes.

Caffeine at work

There is a large literature on the effects of caffeine on performance. Most of the studies have been conducted in the laboratory and further information is required on the effects of caffeine consumption on performance and safety at work. The present studies aimed to determine whether the level of caffeine consumption influenced changes in alertness and performance over the working day. Secondary analyses of a large epidemiological database were also conducted to examine associations between caffeine consumption and cognitive failures and accidents at work. In the first study 110 volunteers, all of whom were regular caffeine consumers, rated their alertness and carried out a simple reaction time task before and after work on a Monday and Friday. Caffeine consumption during the day was recorded and volunteers were sub-divided into low and high consumers on the basis of a median split (220 mg/day). The second study involved secondary analyses of a database formed by combining the Bristol Stress and Health at Work and Cardiff Health and Safety at Work studies. In the first analyses associations between caffeine consumption and frequency of cognitive failures were examined in a sample of 1253 white-collar workers. The second set of analyses examined associations between caffeine consumption and accidents at work in a sample of 1555 workers who were especially at risk of having an accident. The results from the first study showed that those who consumed higher levels of caffeine reported significantly greater increases in alertness over the working day and a significantly smaller slowing of reaction time. The results from the second study demonstrated significant associations between caffeine consumption and fewer cognitive failures and accidents at work. After controlling for possible confounding factors it was found that higher caffeine consumption was associated with about half the risk of frequent/very frequent cognitive failures and a similar reduction in risk for accidents at work. Overall, the results from the three analyses show that caffeine consumption may have benefits for performance and safety at work.

Caffeine Intake and Delayed Conception

The European Study Group on Infertility and Subfecundity; Department of Public Health, Alicante University, Spain; Danish Epidemiology Science Centre and Department of Epidemiology and Social Medicine, Aarhus University, Denmark; and Regione Lombardia, Servizio Epidemiologia e Sistema Informativo, Milano, Italy. Am J Epidemiol 1997;145:324-334.

Caffeine intake and delayed conception: a European multicenter study on infertility and subfecundity. European Study Group on Infertility Subfecundity.

The effects of caffeine consumption on delayed conception were evaluated in a European multicenter study on risk factors of infertility. Information was collected retrospectively on time of unprotected intercourse for the first pregnancy and the most recent waiting time episode in a randomly selected sample of 3,187 women aged 25-44 years from five European countries (Denmark, Germany, Italy, Poland, and Spain) between August 1991 and February 1993. The consumption of caffeinated beverages at the beginning of the waiting time was used to estimate daily caffeine intake, which was categorized as 0-100, 101-300, 301-500, and > or = 501 mg. Risk of subfecundity (> or = 9.5 months) and the fecundability ratio, respectively, were assessed by logistic regression and Cox proportional hazard analyses, adjusting for age, parity, smoking, alcohol consumption, frequency of intercourse, educational level, working status, use of oral contraceptives, and country. A significantly increased odds ratio (OR) of 1.45 (95% confidence interval (CI) 1.03-2.04) for subfecundity in the first pregnancy was observed for women drinking more than 500 mg of caffeine per day, the effect being relatively stronger in smokers (OR = 1.56, 95% CI 0.92-2.63) than in nonsmokers (OR = 1.38, 95% CI 0.85-2.23). Women in the highest level of consumption had an increase in the time leading to the first pregnancy of 11% (hazard ratio = 0.90, 95% CI 0.78-1.03). These associations were observed consistently in all countries as well as for the most recent waiting time episode. The authors conclude that high levels of caffeine intake may delay conception among fertile women.

Caffeine and bone loss in healthy postmenopausal women

The effects of caffeine consumption on rates of change in bone mineral density (BMD) were examined in 205 healthy, nonsmoking, postmenopausal women. BMD of the spine and total body were measured by dual-energy x-ray absorptiometry, and dietary intakes by food-frequency questionnaire. Among women with calcium intakes above the median (744 mg/d), 1-y rates of bone change--adjusted for years since menopause, body mass index, physical activity, and baseline BMD--did not differ by caffeine intake. However, among women consuming less calcium, those with the highest caffeine intakes (> 450 mg/d) had significantly more bone loss (ANCOVA, P < 0.05) than did women consuming less caffeine (0-171 and 182-419 mg/d). Percent change in BMD by lowest to highest tertile of caffeine consumption was 0.26 +/- 2.74, 0.70 +/- 2.70, and -1.36 +/- 2.70 at the spine and -0.19 +/- 1.24, 0.23 +/- 1.23, and -0.68 +/- 1.25 at the total body. Daily consumption of caffeine in amounts equal to or greater than that obtained from about two to three servings of brewed coffee may accelerate bone loss from the spine and total body in women with calcium intakes below the recommended dietary allowance of 800 mg.

Biochemical changes in the exocrine pancreas of rats fed caffeine.

Coffee consumption has been associated with pancreatic disorders, but the mechanisms involved remain to be elucidated. This investigation examines the effects of caffeine consumption on the structure and function of the exocrine pancreas. Groups of rats, fed ad libitum commercial laboratory diet, were given drinking water which contained either caffeine (0.09 mg/ml) or nothing at all. The rats were allowed drink ad libitum and were killed 6 weeks later. Final body and pancreatic weights were not significantly different between the groups at the end of the experimental period. Although no ultrastructural effects of caffeine on the pancreas were observed, amylase and trypsinogen activity was 35% higher in pancreatic homogenates from caffeine-fed rats compared with controls. In addition, levels of immunoreactive cationic trypsin(ogen) were 41% higher than control levels in pancreases from the caffeine-fed rats. Also, the circulating levels of amylase and immunoreactive cationic trypsin(ogen) in serum were lower in the caffeine group compared with controls. When dispersed pancreatic acini isolated from the caffeine-fed rats were incubated in vitro with increasing concentrations of CCK-8 or nicotine, the rate of release of amylase, trypsinogen, and chymotrypsinogen was lower than in the control rats. This effect did not appear to be due to inhibition of protein synthesis, as determined by [3H]leucine incorporation into acinar protein. These data suggest that prolonged intake of caffeine at common dietary levels inhibits pancreatic enzyme secretion.

Effects of caffeine consumption on nicotine consumption.

Coffee-drinking cigarette smokers take in more nicotine when they ingest almost no caffeine than when they ingest an amount of caffeine ranging from 75 mg to 300 mg. They do not take in relatively less nicotine as the dose of caffeine increases from 75 mg to 300 mg. It seems, then, that something due to caffeine deficit is responsible for the effect. Heavier users of caffeine show this effect less strongly than do lighter users of caffeine. These results are discussed in terms of the discriminability of caffeine and nicotine deficits and the possible influence of differential tolerance to caffeine. The importance of evaluating caffeine consumption when studying nicotine use and the importance of considering the chronic level and use of these drugs when studying their effects on behavior is indicated.