Because of prohibition, probably most young cannabis users in the UK know of only two kinds of cannabis: “solid” or “Green”, by which they mean low grade hash or herbal. Despite a whole generation of cannabis use, people are generally more ignorant about what is on offer now than they ever were.

In truth, as anyone with a wider knowledge of the plant will tell you, cannabis comes in many different strains, each with subtly – and sometimes not so subtle – differences in effect. Some strains can be described as “trippy”, or “edgy” whilst other “laid back”, “spacey” and so on. Back in the day hashish imported to the UK from Morocco (the real stuff, not this awful product of prohibition called soapbar) was well understood to be very different from Thai grass for example. This difference wasn’t simply one of strength as such, it was a real difference in what cannabis actually did to the user. Good old “Rocky” hash would get you very stoned, but in a different way to Thai weed.

Reading reports in the popular press you could be forgiven for thinking the only issue of any importance was the level of THC in a sample. As with booze, it’s generally presented as a simple issue of strength with claims that “modern” strains of cannabis are “stronger” than the old forms. This is a huge and very misleading distortion of he truth which is perhaps finally beginning to change.

Cannabis is not simply delta 9-tetrahydrocannabinol (THC), that drug may well produce the “main” effects that cannabis is well known for, but it isn’t the whole story. Indeed, THC taken alone as a pure substance has long been known to have somewhat unpleasant effects. In recent years the role of another chemical in cannabis has began to attract attention, cannabidiol or CBD.

CBD is an interesting substance in that it doesn’t seem to have any intoxicating effect in its own right, but does exhibit some good anti psychotic properties as research by Markus Leweke in Germany has shown (Guardian report from last year). The claim is that different strains of cannabis contain different ratios of THC and CBD, hence their differing effects.

Actually it should be pointed out that cannabis contains much more in the way of psychoactive compounds than just THC and CBD, but these two are probably the most important.

What this boils down to is that strength is not the only – probably not the most – important aspect of cannabis. The ratio of THC to CBD is probably far more important, especially if there is truth in the claims of psychotic problems linked to cannabis use.

So it was interesting to see a report of a small study undertaken by Celia Morgan and H Valerie Curran, from University College London reported on psychiatrysource.com originally published in the British Journal of Psychiatry

Hair samples of subjects were analysed using gas chromatography/mass spectrometry for the presence of cannabinoids. In order to assess psychosis proneness, the team administered the short form of the Oxford Liverpool Inventory of Life Experiences (OLIFE) questionnaire and Peter’s Delusion Inventory (PDI) was used to examine delusional thinking amongst the sample group.

The results support what experienced stoners already knew:

The implications of these findings are that people who smoke different strains of cannabis manifest different psychological symptoms.”

Isn’t science wonderful? Sorry for the sarcasm but they didn’t really need to use gas chromatography to discover that. However, they go on to speculate that

“Moreover, this suggests that smoking strains of cannabis containing CBD in addition to THC may be protective against the psychotic-like symptoms induced by THC alone.”

Which can only support the need to properly regulate the cannabis market so that people know which strain they’re getting. Clearly, if the only choice is between “solid” and “green”, this can’t happen.

But a health warning over this research. They examined just 140 people, so the sample is very small. Of these 85 had no cannabinoids in the hair, 27 with THC+CBD, 20 with THC only and 8 with CBD only. Their results were extrapolated from the observations made of the 20 THC only people compared with the 27 THC/CBD subjects and 85 no cannabinoids subjects. Worse, we’re told that

The eight individuals who screened positive for CBD only in their hair were excluded due to the small number.

Pardon? 8 is not that small a sample when you’re working with figures like 20. More than that however, where on earth did they find subjects who had been smoking cannabis with only CBD in and no THC? Frankly, that isn’t very likely. Remember, these are hair samples which by their nature will be providing a time averaged sample, so to test positive for CBD only would surely mean they’ve been using cannabis only containing CBD for some time.

By the same token it seems unlikely they would have found people who had been using pure THC either, even the worst Daily Mail killer skunk has some CBD in it.

The existence of this “CBD only” group of results more likely shows a problem with the methods used in the study, in particular the assumption that traces in hair samples do actually reflect the past use of specific strains of cannabis. If so, that undermines what at first sight was a promising finding.
Sadly the original document is only available with a subscription to The British Journal of Psychiatry. If any reader has access to this study, UKCIA would love to see it.
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Edited to add UKCIA was sent a link to the paper. The study was based on subjects taking part in an other study which involved groups

categorised as current and former ketamine users, other drug users and non-users.

We are not told what other drugs they used, which of course could more than account for the claimed observations.

The paper also claims that:

there are higher levels of D9-THC in ‘skunk’ or genetically modified strains of the plant.

There is no “genetically modified” cannabis of course.

Read it for yourselves