The NHS reports that 6% of UK teenagers used cannabis in 2023.[1]
When asked, teens say they’re not worried about the long-term effects of their cannabis use, but their concerned parents and teachers might be on to something.
Research into cannabis and brain development shows that the effects of weed on the adolescent brain are much more magnified compared with adults, harming mental health, memory and IQ, and this damage can even be long-lasting.
The adolescent brain is still developing, so drugs and alcohol affect teenagers more intensely and for far longer than they affect an adult.
Studies show that the active chemicals in weed have one common outcome – structural changes in the brain.
While our brains never stop growing and changing, the brain goes through far more significant changes until 15-18 than at any time after this age.[2]
At fifteen, the prefrontal cortex of the brain is going through major updates.
This is the part that’s responsible for making decisions, controlling impulses, and thinking things through. In fact, our brains continue to ‘rewire’ through synaptic pruning well into our 20s.
Weed contains over 500 chemicals, but the main mind-altering element is a psychoactive compound called THC (delta-9-tetrahydrocannabinol).
THC interacts with the endocannabinoid system – the part of our brain responsible for emotional and nervous system regulation. When this system is disrupted, it can negatively affect mood, memory, and motivation.
Adolescent brains are in a state of neuromaturation. Cannabis can therefore have more profound effects:
These effects can be long or short-term.
Teens taking weed will notice that symptoms don’t just affect them while they’re high; there are a few physical and mental effects that last long after the weed has worn off.
When weed enters your system, you’ll feel the ‘high’ of the drug. This may give you the pleasurable effects like relaxation and entertainment, but it can also cause negative symptoms:
Cannabis can negatively affect how you feel or act:
Your school or learning could suffer if you smoke weed:
Using cannabis as a teenager can cause long-term negative changes to your memory and mental health that may never go away. There’s no safe limit for the amount of weed you can take before harm begins.
Using weed at a young age can inhibit your ability to form new memories, especially if you take a high dose or use it often. Weed use causes thinning of the cerebral cortex, which can lead to attentional impulsiveness.
When studied, adolescents aged 13 to 14 years old who had used cannabis scored lower on an episodic memory task (long-term memory of personal events). The more cannabis used, the more likely you are to struggle with memory tasks.
Another small study found that people who were frequent pot smokers by their 18th birthday and continued with heavy use lost 8 IQ points.[3]
Weed has been linked to:
Many people report seeing shadow people when high on weed. This is a hallucination where you imagine dark figures in your peripheral vision. They’re usually seen while experiencing paranoia, which is a symptom of cannabis use.
These issues can all lead to low motivation, apathy, struggling with school or work, lower chances of finishing school, relationship problems and ultimately, poorer life satisfaction.
Yes, research tells us that the earlier you start using weed, the more likely you are to become addicted. Early-onset weed users are 2–5 times more likely to experience drug dependence later in life.
Cannabis use disorder is a psychiatric disorder brought on by frequent cannabis use. This is when you begin to feel your life is consumed by weed, and your cravings begin to overcome your willpower.
The symptoms include:
It can be concerning to be the parent or guardian of a teenager who is showing signs of uncharacteristic behaviour, or who is interested in weed or drug paraphernalia.
It’s important to spot cannabis use in teenagers early and support them in the right way.
First, you need to get an understanding of whether your child is using weed, and how often that may be.
An unusual drop in grades, sudden changes in behaviour, social withdrawal or using weed to cope emotionally are all signs that your child’s weed use may be getting out of hand.
Weed intoxication and use can look like:
If you think your child is using cannabis, try to be open and curious, focus on health instead of punishment, and avoid scare-mongering.
Getting early support is the best way to prevent long-term harm, and there are lots of NHS and free support services available for weed addiction.
Speak to your GP, who will assess your health and give you local information about addiction services in your area, or talk to your school counsellor.
Whether you’re worried about your own weed addiction or a loved one, our advisors can offer you free advice and support as well as referrals to top rehabs throughout the UK.
For more help with cannabis addiction, call 0800 140 4690 (or +44 345 222 3508 from outside the UK).
Below, we answer common questions around this important topic:
Heavy weed use in adolescence can cause long-lasting damage to the brain, particularly learning, attention and memory. Results will vary from person to person, and stopping weed early can allow the brain to recover.
Vaping is not safer, and poses its own risks like lung damage. THC is present in all cannabis, and it’s this active ingredient that has been shown to cause harm to the brain and mental health of teenagers.
Taking a lower dose of weed lowers the risk of harm, but there is no limit which is completely safe, particularly in the growing brains of teenagers. There is no research which has shown occasional use to be harmless.
Memory and attention have been shown to recover within a few weeks of stopping weed. Brain fog will gradually lift, and your brain’s hippocampal volume should restore. However, teenagers need to be particularly careful, as damage can be more long-lasting.
[2] https://www.cell.com/neuron/fulltext/S0896-6273(16)30809-1
[3] https://www.pnas.org/doi/abs/10.1073/pnas.1206820109
Boris is our editor-in-chief at Rehab 4 Addiction. Boris is an addiction expert with more than 20 years in the field. His expertise covers a broad of topics relating to addiction, rehab and recovery. Boris is an addiction therapist and assists in the alcohol detox and rehab process. Boris has been featured on a variety of websites, including the BBC, Verywell Mind and Healthline. You can connect with Boris online at LinkedIn or X.com.
