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Cannabis: the facts

How cannabis affects you, the risks, plus where to find help if you are trying to quit weed.

Cannabis (also known as marijuana, weed, pot, dope or grass) is the most widely used illegal drug in the UK.

The effects of cannabis vary from person to person:

  • you may feel chilled out, relaxed and happy
  • some people get the giggles or become more talkative
  • hunger pangs ("the munchies") are common
  • colours may look more intense and music may sound better
  • time may feel like it's slowing down

Cannabis can have other effects too:

  • if you're not used to it, you may feel faint or sick
  • it can make you sleepy and lethargic
  • it can affect your memory
  • it makes some people feel confused, anxious or paranoid, and some experience panic attacks and hallucinations – this is more common with stronger forms of cannabis like skunk or sinsemilla
  • it interferes with your ability to drive safely

If you use cannabis regularly, it can make you demotivated and uninterested in other things going on in your life, such as education or work.

Long-term use can affect your ability to learn and concentrate.

Can you get addicted to cannabis?

Research shows that 10% of regular cannabis users become dependent on it. Your risk of getting addicted is higher if you start using it in your teens or use it every day.

As with other addictive drugs, such as cocaine and heroin, you can develop a tolerance to cannabis. This means you need more to get the same effect.

If you stop using it, you may get withdrawal symptoms, such as cravings, difficulty sleeping, mood swings, irritability and restlessness.

If you smoke cannabis with tobacco, you're likely to get addicted to nicotine and risk getting tobacco-related diseases such as cancer and coronary heart disease.

If you cut down or give up, you will experience withdrawal from nicotine as well as cannabis.

See tips for stopping smoking.

Cannabis and mental health

Regular cannabis use increases your risk of developing a psychotic illness, such as schizophrenia. A psychotic illness is one where you have hallucinations (seeing things that aren't really there) and delusions (believing things that aren't really true).

Your risk of developing a psychotic illness is higher if:

  • you start using cannabis at a young age
  • you smoke stronger types, such as skunk
  • you smoke it regularly
  • you use it for a long time
  • you smoke cannabis and also have other risk factors for schizophrenia, such as a family history of the illness

Cannabis also increases the risk of a relapse in people who already have schizophrenia, and it can make psychotic symptoms worse.

Other risks of cannabis

Cannabis can be harmful to your lungs

People who smoke cannabis regularly are more likely to have bronchitis (where the lining of your lungs gets irritated and inflamed).

Like tobacco smoke, cannabis smoke contains cancer-causing chemicals, but it's not clear whether this raises your risk of cancer.

If you mix cannabis with tobacco to smoke it, you risk getting tobacco-related lung diseases, such as lung cancer and chronic pulmonary obstructive disease (COPD).

You're more likely to be injured in a road traffic accident

If you drive while under the influence of cannabis, you're more likely to be involved in an accident. This is one reason why drug driving, like drink driving, is illegal.

Cannabis may affect your fertility

Research in animals suggests that cannabis can interfere with sperm production in males and ovulation in females.

If you're pregnant, cannabis may harm your unborn baby

Research suggests that using cannabis regularly during pregnancy could affect your baby's brain development.

Regularly smoking cannabis with tobacco increases the risk of your baby being born small or premature.

Cannabis increases your risk of cardiovascular disease and stroke

If you smoke it regularly for a long time, cannabis raises your chances of developing these conditions.

Research suggests it's the cannabis smoke that increases the risk, not the active ingredients in the plant itself.

Does my age affect my risks?

Your risk of harm from cannabis, including the risk of schizophrenia, is higher if you start using it regularly in your teens.

One reason for this is that, during the teenage years, your brain is still growing and forming its connections, and cannabis interferes with this process.

Does cannabis have medicinal benefits?

Cannabis contains active ingredients called cannabinoids. Two of these – tetrahydrocannabinol (THC) and cannabidiol (CBD) – are the active ingredients of a prescription drug called Sativex. This is used to relieve the pain of muscle spasms in multiple sclerosis.

Another cannabinoid drug, called Nabilone, is sometimes used to relieve sickness in people having chemotherapy for cancer.

Trials are under way to test cannabis-based drugs for other conditions including cancer pain, the eye disease glaucoma, appetite loss in people with HIV or AIDS, and epilepsy in children.

We won't know whether these treatments are effective until the trials have finished.

Read more about clinical trials

Trying to give up?

If you need support with giving up cannabis:

You'll find more information about cannabis on the Frank website.

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