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Cannabis, skunk and the teenage brain


Photo: Dierk Schaefer 

Consultant addiction psychiatrist Dr Adam Winstock offers parents advice on a drug that is widely used by UK teenagers and has been linked in the media to young people’s mental health issues.

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Cannabis is still the world’s most popular illegal drug worldwide, but in the UK, its use is falling. For most people, cannabis is not a source of harm and is used to achieve a feeling of being relaxed and high. Most people use it for a few years then stop.  Other people don’t stop and – as with all drugs – the more you use, and the longer you use for, the more likely you are to run into problems.  

As has happened with tobacco, increasingly people seem to be more aware of the risks of using cannabis (especially of smoking it) and are making a choice not to use.  

Is cannabis stronger now?

Cannabis has changed a lot over the last 20 years.  The most common form is a strong herbal preparation often called ‘skunk’ or ‘hydro’.  Skunk is different from resin and from normal bush or commercial weed in that it has lots of one cannabis chemical – THC (about 8-14%) – and very little of another calming and relaxing cannabis chemical called CBD. Resin or normal weed has a balance of both chemicals and lower levels (about 2-4% each). 

Skunk is the form used by over 80% of UK users and, as well as being the commonest form, is also the most expensive. And while it seems to be preferred by most people to other types like hash or resin (the usually black/brown waxy/squidgy form of the drug), it also causes more memory loss, dependence and paranoia. 

The side-effects of cannabis

Cannabis makes many people feel relaxed and high but others can get anxious, panicky and worried about what other people are thinking about them. Mixed with alcohol, cannabis can make you feel sick. Some people become dependent on cannabis – yes, really – about one in 10, who often smoke every day and can smoke very large amounts of cannabis without getting very stoned. They spend a lot of money (skunk costs about £10 per gram, or £250-300 per ounce).

‘People who start taking cannabis at a young age have a much higher risk of becoming dependent’

They find they can’t stop and when they try, they can’t sleep, they get irritable, miserable and sometimes, angry. People who start taking cannabis at a young age have a much higher risk of becoming dependent. 

Most people who use cannabis in the UK mix it with tobacco and smoke it in a joint. Smoking cannabis is bad for your lungs in a similar way to tobacco (and can lead to cancer, chronic bronchitis and emphysema). Trying to stop both cannabis and tobacco is harder that trying to quit if you use just one of these drugs. Eating the drug can reduce some risks but can also lead to people's getting very, very stoned and feeling frightened because the effect comes on slowly but lasts a long time. (It can take up to two hours for users to feel any effect after eating cannabis but this can then last for eight to 12 hours.)

While many people don’t have any trouble with cannabis and enjoy using it, some people do have problems. It is not easy to predict who will and who won’t encounter difficulties as a result of their use, but there are some warning signs and circumstances that make people more vulnerable.

What teenagers should know about cannabis

The younger you start, the more likely you are to develop dependence and experience mental health difficulties and problems at school. Using cannabis before the age of 18 and, especially, before the age of 16, is particularly risky and seems to make people less smart (yep, it could drop your IQ a few points).

‘The young brain is still developing and that seems to make it more vulnerable to drugs’

This is because the young brain is still developing and that seems to make it more vulnerable to drugs. So the best advice is that before you expand your brain, you should let it stop growing.  

Now, it’s also true that many young people who run into problems have other difficulties – at home, at school and with their mental health. Cannabis may not be the biggest problem but, for many of them, cannabis can make it harder to sort out those other issues. 

Other risk factors include having someone in the family with a serious mental illness, like schizophrenia or bipolar affective disorder. People who already have a mental illness are those who are most likely to experience problems with cannabis: it tends to make things worse, not better. While some people say cannabis helps them to feel better, for most it actually can stop medication working and they tend to feel brighter and less depressed when they stop. 

Warning signs that someone might be vulnerable to cannabis-related harm include

  • Feelings of anxiousness or paranoia when they use.
  • Finding that they are using more than they want to.
  • Being stoned is interfering with other things in their life, like school friends and family. 

What parents can do

If you want to help someone cut down then suggest they:

  • Start using later in the day.
  • Don’t use lots of tobacco.
  • Spend more time with non-using friends.
  • Cut down on tea, coffee and caffeine drinks, as these make withdrawal worse, especially problems with sleeping, which should get better after a week or so. 

Encourage them to:

  • Chat to people they trust and ask them to help.
  • Get some patches for the tobacco addiction (but take them off a night)
  • Go and see their GP if they are finding it hard to reduce their usage. 

Further reading

To help your child reduce their risk from cannabis, get them to check out the Global Drug Survey Highway Code ( 

It’s possible to check out how someone’s use of cannabis compares to tens of thousands of other users with the cannabis drugs meter app on Google Play or at

Cannabis use and youth: a parent’s guide. Information from Here To Help

The advice published on Parent Info is provided by independent experts in their field and not necessarily the views of Parent Zone or NCA-CEOP.

Updated: ​May 2018

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