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Cannabis: the facts - Healthy body

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

The effects of cannabis can vary a lot from person to person. It can also vary depending on how much or how often it's taken and what it contains.

Some examples include:

  • feeling chilled out, relaxed and happy
  • laughing more or become more talkative
  • feeling hunger pangs ("the munchies")
  • feeling drowsy, tired or lethargic
  • feeling faint or sick
  • having problems with memory or concentrating
  • experiencing mild hallucinations
  • feeling confused, anxious or paranoid

Can you get addicted to cannabis?

It's possible to get addicted to cannabis, especially people who are considered regular or heavy users.

If regular users stop taking cannabis, they may get withdrawal symptoms, such as feeling moody and irritable, feeling sick, difficulty sleeping, difficulty eating, sweating, shaking and diarrhoea.

Regularly smoking cannabis with tobacco also increases the risk of becoming addicted to nicotine and experiencing withdrawal symptoms from nicotine as well as cannabis if you cut down or give up.

Regularly using tobacco also increases the risk of tobacco-related diseases such as cancer and coronary heart disease.

See tips for stopping smoking

Trying to give up cannabis?

If you need support with giving up cannabis:

  • see a GP
  • visit Frank's Find support page
  • call Frank's free drugs helpline on 0300 123 6600
  • see Drug addiction: where to get help
  • Marijuana Anonymous is a free self-help group. Its "12 step" programme involves stopping using marijuana with the help of regular face-to-face and online support groups. You can call them on 0300 124 0373 (callback service).

Read more information about cannabis on the Frank website

Cannabis and mental health

Regular cannabis use increases the risk of developing a psychotic illness, such as schizophrenia.

A psychotic illness is one where you have hallucinations (seeing things that are not really there) and delusions (believing things that are not really true).

The risk of developing a psychotic illness is higher in people who:

  • start using cannabis at a young age
  • smoke stronger types, such as skunk
  • smoke it regularly
  • use it for a long time
  • 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

Other risks of regularly using cannabis can include:

  • feeling wheezy or out of breath
  • developing an uncomfortable or painful cough
  • making symptoms of asthma worse in people with asthma
  • reduced ability to drive or operate machinery safely

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 and pregnancy

Cannabis use may affect fertility. Regular or heavy cannabis use has been linked to changes in the female menstrual cycle and lower sperm count, or lower sperm quality in men.

Using cannabis while pregnant may harm the unborn baby. Cannabis smoke contains many of the same harmful chemicals found in cigarette smoke.

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

Cannabis has not been linked to birth defects, but research suggests that using cannabis regularly during pregnancy could affect a baby's brain development as they get older.

Does cannabis have medicinal benefits?

Cannabis contains active ingredients called cannabinoids. 2 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.

Clinical 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.

Read the latest updates on cannabis, cannabinoids and cancer – the evidence so far on the Cancer Research UK website.

Page last reviewed: 3 December 2020
Next review due: 3 December 2023