09 May Potency: A Widely Misunderstood Concept

A study by Dr Zerrin Atakan and Prof Philip McGuire from 2009 threw some light on the way cannabis actually works by looking at the effects of THC and CBD – the two principal components of cannabis.

The fact that there are two major active components has meant the nature of cannabis has been seriously misrepresented and therefore misunderstood for years, originally through ignorance but more recently deliberately.

For just about all other drugs of intoxication (or enlightenment depending on how you look at these things) there’s really only one consideration: How much of the drug you take, i.e. the dose. Strong drugs simply give you more of the drug per gram, pint or whatever unit the drug is measured in. In other words, drugs generally consist of an active compound contained within a larger volume of something else which can be considered neutral.

Hence we have a very simple variable to talk about which we call “strength”. Even if they don’t really understand how it works, most people are familiar enough with this concept as it applies to booze and understand that a beer with a 3% ABV is a lot weaker than a beer with 10% ABV, even if they don’t know what a “% ABV” actually means*. Most people know something else about “strength” as well, which is that you don’t need as much of the strong stuff as you do the weak, but have enough of the weak stuff and you end up in the same place as you do with the strong stuff more or less.

Hence we have a simple variable called “strength” which is widely understood and is nice and easy. This concept extends way beyond booze to include all the naughty drugs – cocaine, ecstasy, heroin, you name it the same logic applies, “stronger” means “higher dose” per gulp/snort/fix.

But when we come to consider cannabis we find things are measured differently and we find a new word is used: “potency”. Whenever governments or their agencies start using a subtly different term for something you think you understand it’s always a good idea to ask why?

The Home Office study into cannabis potency of 2008 (PDF read it here) had a go at defining this “potency” concept. The definition the study gave was:

The potency of cannabis is defined as the concentration (%) of delta 9-tetrahydrocannabinol (THC)

Sadly it didn’t specify what the concentration is a percentage of, giving the misleading impression perhaps that a sample of herbal cannabis consists of upwards of 40% THC. Now, this is clearly not the case as a sample of herbal plant material plainly doesn’t consist of nearly half THC, either by volume or by weight. No matter how strong the cannabis is, most of it is clearly plant material. Indeed, it’s pretty obvious that it doesn’t even consist of 5% THC by weight or volume because that would still be a huge amount of what is a very powerful psychoactive drug. So it’s clear that “potency” isn’t anything like the same simple concept as strength.

Actually the % THC figure is the proportion of THC in the oils produced by the plant. The plant oozes oils – the pure resin – from glands known as “trichomes”. It’s these tiny beads of oil which contain the active chemicals that make cannabis what it is and the “potency” figure often quoted is the proportion of this oil which is THC.

Two important points flow from this:

1: Potency is not strength. Clearly you could have a sample of cannabis with very few globs of resin on, which would make it quite weak, although the resin it did contain could be high in THC, making it a high potency. Likewise a concentrated form of low potency cannabis could deliver a large dose of THC, making it quite strong. One “concentrated form of cannabis” is known as hashish, being the resin of the plant with far less vegetable matter included.

2: The THC is expressed as a percentage (by weight actually) of the oils, there are clearly other substances in the oil, quite a few of which are psycho active but it turns out that one in particular, known as CBD or cannabidiol, is very important when it comes to understanding just what cannabis does to the user.

Spurred on by the Reefer Madness V2 scare of the last decade there were two “Cannabis and Mental Health” conferences held in London in 2004 and 2007 and one of the more interesting presentations (for me) came from Dr Zerrin Atakan who was involved in a study which reported in 2009 called “Distinct Effects of Delta-9-Tetrahydrocannabinol and Cannabidiol” on Neural Activation During Emotional Processing”. The study undertaken by Zerrin Atakan and Professor Philip McGuire consisted of giving subjects a dose of THC or CBD or a placebo and examining the effects on the subject by both a series of standard tests and also by magnetic resonance imaging of the brain (here). Professor Philip McGuire stated

“These studies show that THC and CBD have distinct effects on brain function in humans, and these may underlie their correspondingly different effects on cognition and psychiatric symptoms. Determining how the constituents of cannabis act on the brain is fundamental to understanding the role of cannabis use in the aetiology of psychiatric disorders.”

In English this means understanding the combined roles of THC and CBD is important for understanding how cannabis works and what its effect on the brain will be; it isn’t just about THC,

The really interesting thing about this is that CBD turns out to be playing a significant role, yet until recently it had never been routinely measured. It’s almost the polar opposite of THC in its effects in some respects; if THC is linked to psychotic type episodes, CBD has anti psychotic properties. If THC is thought to cause panic attacks, CBD calms those impulses. Put in terms the Daily Mail could understand, if THC is “bad”, CBD is “good”.

The practical upshot of all this is that talking of cannabis simply in terms of “potency” masquerading as “strength” is meaningless, we need to be far more sophisticated in the way to describe it. The measure of “potency” as used by the government is simply not up to the job, which is no surprise really as it came from the law enforcement requirements of prohibition, not from concerns of public health or any real understanding of the plant. To mean anything, “potency” has to state the concentration of both THC and CBD.

Of course, all this isn’t news to experienced cannabis users. It’s long been known that the old skool hash from Morocco for example was laid back and dreamy whilst some of the modern strains are somewhat “edgy” or “trippy”. But we can thank Zerrin and her team for providing the explanation in terms of the combined effects of THC and CBD on the brain and providing the science, this difference is real.

Now the the Home Office “potency” study of 2008 was close to being “cod science” because of the way it collected its data and on its lax definitions of potency but it did show one interesting result which is relevant to this discussion; the THC/CBD balance of “traditional” hashish we used to get in the UK is very different to that of some herbal cannabis on sale today. The traditional hash contained something like 5% THC and 3.5% CBD on average. Now what this means is the oils in the sample contained a total of 8.5% active ingredients and 91.5% uninteresting goo – ie mostly none psycho-active resin plus a range of minor active chemicals. The valuable bit of information here isn’t the THC concentration but the ratio of the two chemicals of 7 parts CBD to 10 parts THC. That isn’t too far off 50-50. It’s interesting to note that the composition of Sativex – the cannabis medicine – is 51/49 THC/CBD, a composition arrived at because it had the best effectivity with the minimum unpleasant side effects.

The thing to note is that before the present prohibition policy choked off imported hash from north Africa, most of the cannabis supplied to the UK was of this type with a more or less equal ratio of THC:CBD. The policy so enthusiastically followed by our government has seen this replaced by strains which are much lower in CBD. So there we have an “unintended consequence” of prohibition, the suppression of a well balanced product and its substitution with something very different, but different in a way no-one thought important to monitor, much less control.

This is at the root of the claims that cannabis potency has increased in recent years, which is a claim often made by prohibition campaigners and used to justify continued prohibition. Far from being an argument in favour of continued prohibition however, this change was caused by it. If as the government claims it is true that high potency (ie low CBD) cannabis is dangerous for some people it is a danger caused directly by the prohibition policy.

With most – if not all – other drugs the control of the strength is important. With cannabis the composition in terms of THC and CBD is equally if not more important. This variable is determined primarily by the strain grown, in other words by the seeds sold, but also to an extent by the maturity of the plant when harvested. If the government is really concerned about the potential for harm caused by the type of cannabis on sale in the country as they claim to be, controlling and properly regulating the seed suppliers and the growing industry is the way to go. Here we have some solid science to support that suggestion.

Thus far, the law has only served to make things potentially more dangerous whilst relying on a useless measurement which is widely misunderstood, but that’s how prohibition works.


* % ABV means “the percentage of Alcohol by volume”, so 100 ml of 10%ABV plonk will contain 10ml of pure alcohol.

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