Donders Wonders

What does cannabis addiction do to the brain?

This post is also available in Dutch.

Using cannabis is fairly ‘normal’ in the Netherlands and some other countries, but how does overuse affect our brain and behaviour?

A marijuana-tobacco joint. Image by Monotoom (own work) [CC BY 3.0], via Wikimedia Commons.

The Netherlands is known for its policy of tolerance with regard to weed. You can buy, smoke and even grow limited amounts of it. Cannabis, like other drugs, stimulates the release of dopamine in specific brain areas, resulting in a sense of reward. Quite a lot is known about this soft drug (here: general facts (Dutch), health effects (Dutch) and current figures from the Trimbos Institute (Dutch)). However, the effects of excessive long-term use on the brain are still relatively unravelled.

Facts on the use of cannabis in the Netherlands
According to the Trimbos Institute’s 2016 report, more than 25% of cannabis users smoke weed (almost) every day. About 8.7% of people between the ages of 15-64 use cannabis sometimes, which is a lot higher than the estimated average for the EU of 6.6%.

More negative emotions among cannabis users
Psychological research has shown that cannabis ‘abusers’ (people for whom use has become problematic (Dutch)) often have altered emotional experiences, involving less positive – and more negative emotions. This often leads to people responding less well to rewards, experiencing more motivational problems and being more sensitive to stress.

Inhibited dopamine activation in cannabis abusers
To look into what effects the abuse of cannabis has on the brain, neuroscientists compared the brains of cannabis abusers and non-users in response to a dopamine activation (participants smoked on average 5 days a week, 2-8 joints per day). The investigators used the drug ‘Methylphenidate’ to raise the dopamine levels in the brain (popularly also called ‘Ritalin,’ normally prescribed to treat ADHD. Read more about Ritalin, dopamine and reward here). Compared to non-users, Ritalin had less effects in the cannabis abusers’ behaviour, heart, blood pressure and brains. Overall, dopamine had a similar effect in the two groups, except for some specific differences in the part of the brain related to reward (ventral striatum) where the dopamine stimulating effect of Ritalin was reduced for cannabis abusers. Also, the smaller the effect of Ritalin within this brain region, the more negative emotions and addiction symptoms abusers experienced.

Advice: don’t smoke weed every day, just now and then
So far only a connection has been found between negative emotionality and less dopamine activation in cannabis abusers. There is not enough evidence yet that cannabis abuse causes this as it could also be the other way around: people with less dopamine activation are more prone to using cannabis. Still, these findings provide us with information on the possible brain mechanism that might lead to behavioural changes in cannabis abuse. Like with all soft and hard drugs, excessive long-term use of cannabis is linked to changes in the brain. And these changes definitely have an impact on your behaviour, emotions and thus your life.

Written by Mahur, edited by Annelies, translated by Rowena.

More information:
Source of the neuroscientific investigation article (PNAS)

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