No proof that high-dose cannabis is more addictive

“People who smoke high-potency cannabis inhale more of the drug’s active ingredient, THC,” the Mail Online reports.

The website reports on a small study involving heavy, habitual users of more potent forms of cannabis such as “skunk” – a type of herbal cannabis specifically bred for its potency.

They wanted to see if users who consumed more potent forms of the plant actually used less cannabis per joint or inhale less smoke, to compensate for the drug’s higher strength.

The active ingredient in cannabis is THC (tetrahydrocannabinol). The more THC in cannabis, the more potent it is, and exposure to high levels has been linked to dependency on the drug.

However, one school of thought – called the “potent pot myth” – argues that smokers of high-strength cannabis adjust their intake to compensate for its potency, usually by inhaling less or rolling joints with less cannabis.

The Dutch researchers found that users of strong cannabis did inhale less smoke. However, they were still exposed to higher doses of THC in each joint than smokers of lower potency cannabis.

However, the belief there is some sort of dose-dependent relationship between THC exposure and the risk of dependency remains unproven. 

Where did the story come from?

The study was carried out by researchers from the Netherlands Institute of Mental Health and Addiction, Utrecht; the University of Amsterdam; and the National Institute for Public Health and the Environment (RIVM), Bilthoven. It was funded by ZonMW, a Netherlands organisation for health research and development.

The study was published in the peer-reviewed journal Addiction.

The Mail Online’s claim that smoking more potent cannabis makes you more likely to be addicted was not supported by this study. In fact, it found that participants’ dependency 18 months after the study began was not independently related to how much THC they were exposed to.

What kind of research was this?

This was a study of 98 heavy cannabis users. It aimed to find out whether consumers of stronger cannabis use less of the drug per joint or inhale less smoke to compensate for the potency of the cannabis. It also aimed to find out if these factors had any link to users’ degree of dependency at a later stage.

The study was both cross-sectional and prospective. A cross-sectional study examines all the data at once, meaning it cannot be used to see if one thing follows another. However, it is useful for showing up patterns or links in the data.

A prospective study follows a group of individuals over time, to discover if there is any association between a particular factor (for example, how much smoke is inhaled) and a health outcome (the severity of later cannabis dependency).

The researchers state that about 1 in 10 cannabis users become dependent, and frequent users are at particularly high risk. The addiction potential of cannabis is thought to be linked to exposure to THC (tetrahydrocannabinol), which is its main psychoactive ingredient. It has been suggested that the recent increase of THC concentration in cannabis may increase cannabis dependence.

However, one theory is that people smoking cannabis with a high THC concentration may reduce the total amount of cannabis they use, or adapt their smoking behaviour to titrate (adjust) their THC exposure, meaning they smoke until a satisfactory effect is reached.

They may do this by reducing the dose (grams) of cannabis per joint, cone, bong hit or similar, or by inhaling a smaller volume of THC-containing smoke.

What did the research involve?

Researchers recruited 98 experienced cannabis users, who brought their own cannabis, rolled a joint and smoked it in a natural setting.

The researchers then analysed the content of the joint, its association with smoking behaviour and the link to the severity of cannabis dependency, both at the time and at a follow-up 18 months later.

Participants came from a larger study of 600 frequent cannabis users recruited from legal outlets in the Netherlands, called “coffee-shops”. They were a mixture of frequent cannabis users (using for three or more days a week, for more than 12 months) and those who used cannabis less frequently.

Interviews and assessments took place in a natural setting chosen by participants – usually their homes. Participants were asked to bring along at least one gram of their preferred cannabis, and to roll and smoke a joint in their usual manner.

Researchers measured the cannabis dose per joint (in grams) by weighing the cannabis sample before and after preparation of the joint. Cannabis THC concentration (potency as a percentage) was measured in the remaining sample by laboratory analysis.

The preferred level of cannabis intoxication was assessed with a visual analogue scale (1: “light buzz” to 10: “very stoned/high”).

The estimated monthly THC exposure was also calculated, to see whether cannabis smoking behaviour could predict the intensity of cannabis dependence separately from other factors. This was based on the number of days using cannabis in the past four weeks, the average number of (whole) joints per day using cannabis, the dose of cannabis per joint and THC concentration.

Smoking behaviour – such as how many puffs someone takes, how long each puff lasted, intervals between puffs, how fast they inhale and how much smoke is inhaled – was measured using a special portable device, in which the joint was placed before being lit and smoked by the participant.

The smoking session was stopped when participants had finished the joint, or when they had achieved their desired high and indicated that they would smoke no more within the next 30 minutes.

Finally, they also measured whether any changes in smoking behaviour occurred over the course of a smoking session.

They assessed the intensity of cannabis dependence at the start of the study using a widely recognised diagnostic guideline, and again 18 months after.

They then assessed the association between cannabis potency and the dose of cannabis used, and between smoking behaviour and THC concentration.

They looked at whether the degree of cannabis dependence 18 months later was associated with smoking behaviour, independent of the cannabis dependence at baseline.

What were the basic results?

Researchers found that: 

• the higher the THC concentration in the cannabis (which ranged from 1.10 to 24.70%), the more cannabis in the joint 
• the higher the THC concentration in the joint, the less smoke was inhaled
• smoking behaviour was associated with the severity of dependence 18 months later 
• a monthly THC dose was not independently associated with the degree of dependence 18 months later 

How did the researchers interpret the results?

The researchers conclude that cannabis users with a preference for stronger joints adjust their THC intake to some extent by inhaling less smoke.

However, they say this does not fully compensate for the higher dosages of cannabis used in more potent cannabis. This leads to a higher THC exposure, compared to users that use lower potency cannabis.

They also say that smoking behaviour appears to be a stronger predictor for cannabis dependency than a monthly THC dose.

Conclusion

It is difficult to know what, if any, firm conclusions can be drawn from this small study, which analysed results from a single session of smoking cannabis.

It is possible that factors such as how much cannabis goes into a joint and how much smoke is inhaled will vary according to individual circumstances and mood etc.

It is of note that the participants were not allowed to share the joint with others and were instructed to finish the joint or stop smoking it when they had achieved the desired effect. It is plausible that both instructions would change their normal behaviour.

How these findings relate to cannabis dependency is unclear, as there was no strong, independent association between THC exposure and dependency at a later stage.

There are several factors associated with drug dependency, including genes and family background.

Heavy use of cannabis carries several health risks, including mental health problems.

Further research into the potential effects of long-term THC exposure would be useful; however, due to current legal restrictions, this could be problematic to carry out.