Cannabis potency: the need for global monitoring.

Abstract

In this issue of Addiction, Neisink et al. 1 report data from a systematic cannabis potency monitoring programme conducted in the Netherlands between 2005 and 2015. Following a dramatic rise between 2000 and 2004 2, Δ9-tetrahydrocannabinol (Δ9-THC) decreased modestly (0.22% each year) from 2005 to 2015 1. Cannabidiol (CBD), a cannabinoid which may counteract some of the negative effects of Δ9-THC 3-6, was absent from most samples tested 1. Some possible harms of chronic cannabis use (e.g. dependence, increased risk of psychosis) may be predicted by its cannabinoid profile 7, 8. Longitudinal cannabis monitoring programmes can assist investigations between Δ9-THC and CBD and population indicators of burden and morbidity. For example, Δ9-THC trends in the Netherlands 1, 2 might predict treatment demand for cannabis dependence, which rose between 2000 and 2011 but is now stable or decreasing 9. There are currently few data examining the links between cannabinoid profile and adverse outcomes, so enhanced monitoring programmes would assist in the assessment of this important issue. Rising and/or high Δ9-THC alongside a lack of CBD have been reported in a number of other countries 10-13. However, not all have monitored potency regularly or at all, and some have found no reliable change 14. Potency monitoring may be difficult and impractical in some countries for historical and legislative reasons. For example, in Australia, which has no legal imperative to test for potency, there are no longitudinal data monitoring programmes. The first major Australian study of potency 15 took a decade from design to completion due to difficulty in getting sufficient interest to fund it plus a number of legislative difficulties, yet it raises the same concerns as international data with its findings of very high Δ9-THC and low CBD levels in street-level seizures. It will be important to evaluate the impact of current and proposed regulatory changes, as some have been aimed specifically at cannabis potency. In 2011, calls were made to classify potent (≥ 15% Δ9-THC) cannabis as a ‘hard drug’ in the Netherlands, and Uruguay also proposed an upper limit 16. When cannabis was re-classified as a more harmful drug (from Class C to B) in 2008, the UK Home Office stated: ‘The significant increase in both the market share of higher than average potency cannabis and its actual potency in the last few years in the UK are compelling factors’ 17. Unfortunately, the effects of re-classification on potency are unclear, as the last comparable monitoring study was conducted in 2008 10. Initial results from the United States indicate that legal medical cannabis dispensaries were associated with a 1% rise of Δ9-THC in illicit seized samples 18. The effects of state legalization for pleasure are yet to emerge. However, these changes could facilitate monitoring at the retail level, offering methodological advantages 1, 2 and evaluation of Δ9-THC and CBD trends in conditions of greater consumer choice. At a time when global cannabis policy is rapidly shifting, comprehensive monitoring will be a key step towards investigating the effects of these changes on cannabis products and cannabis users themselves. Tom P. Freeman is funded by the Medical Research Council and declares no competing interests. The National Drug and Alcohol Research Centre at UNSW Australia is supported by funding from the Australian Government under the Substance Misuse Prevention and Service Improvements Grants Fund. Wendy Swift has no competing interests to declare.