Potency of Δ⁹–tetrahydrocannabinol and other cannabinoids in cannabis in England in 2016: Implications for public health and pharmacology

Abstract

In 2005 and 2008, studies reported that cannabis in England had become dominated by the sinsemilla (unseeded female) form. The average potency (Δ -tetrahydrocannabinol [THC] content) of this material had doubled over the previous decade. Cannabis resin then circulating contained approximately equal ratios of THC and cannabidiol (CBD), whereas sinsemilla was almost devoid of CBD. Despite raised health concerns regarding sinsemilla use and the development of psychotic disorders, no update on street cannabis potency has been published since 2008. A total of 995 seized cannabis samples were acquired from the same 5 constabulary areas included in the 2005 study. The differing forms were segregated, and a representative 460 samples analyzed to assess their cannabinoid content using gas chromatography. The resultant median sinsemilla potency of 14.2% THC was similar to that observed in 2005 (13.9%). In each case, sinsemilla contained minimal CBD. Compared with 2005, resin had significantly higher mean THC (6.3%) and lower CBD (2.3%) contents (p < 0.0001). Although the average THC concentration in sinsemilla samples across the 5 constabularies has remained stable since 2005, the availability of this potent form of cannabis has further increased. Moreover, the now rarer resin samples show significantly decreased CBD contents and CBD:THC ratios, leaving the United Kingdom's cannabis street market populated by high-potency varieties of cannabis, which may have concerning implications for public health.

Increasing potency and price of cannabis in Europe, 2006–16

“…However, only three European countries (the Netherlands, Sweden, Croatia) provided eligible data on more than one type of herbal cannabis, and for this reason we did not stratify our analysis by type of herbal cannabis. The estimates we obtained for herbal cannabis potency in Europe lie between previous estimates of high-potency indoor-grown herbal cannabis and imported herbal cannabis in European countries [27,42]. They are also very similar to estimates of all forms of herbal cannabis from the United States during the same time-period, when the proportion of sinsemilla samples increased [41].…”

“…This offers one possible explanation for the increase in herbal cannabis potency observed in Europe. The estimates we obtained for herbal cannabis potency in Europe lie between previous estimates of high-potency indoor-grown herbal cannabis and imported herbal cannabis in European countries [27,42]. One strength of our reporting tool was its ability to capture data on multiple types of herbal cannabis.…”

“…The effects of these changes appear to be evident in the French cannabis market, as documented by a 25-year study of police seizures [23]. Increases in THC concentrations were also detected in resin samples collected from police seizures in the United Kingdom from 2004-05 [18] to 2015-16 [24] and in Italy from 2010 to 2013 [25,26]. Increases in THC concentrations were also detected in resin samples collected from police seizures in the United Kingdom from 2004-05 [18] to 2015-16 [24] and in Italy from 2010 to 2013 [25,26].…”

“…The authors reported a substantial increase in resin potency starting in 2011, driven by the emergence of a new type of resin exceeding 20% THC. Increases in THC concentrations were also detected in resin samples collected from police seizures in the United Kingdom from 2004-05 [18] to 2015-16 [24] and in Italy from 2010 to 2013 [25,26]. By contrast, THC concentrations in imported resin samples purchased from coffee shops in the Netherlands were largely stable in potency, from 2005 to 2015 [27].…”

“…In the Netherlands, domestic herbal cannabis showed a marked increase in THC from 2000 to 2004 [28], followed by a marginal decrease from 2005 to 2015 [27]. In the United Kingdom, the potency of herbal cannabis was broadly similar in 2004-05 [18] compared to 2015-16 [24], but increased each year from 2010 to 2013 [25,26] in Italy and from 1992 to 2016 in France [23]. A meta-analysis of herbal cannabis potency world-wide reported annual increases (mean = 0.21% THC per year) from 1970 to 2009 [29].…”