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Cannabis: the facts – Healthy body

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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.

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).

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

Read about how cannabis (marijuana, weed, dope, pot) affects you, the risks and where to find help if you're trying to quit.

Regular marijuana users may need more anesthesia for medical procedures

Patients getting surgery may need higher levels of anesthesia if they are regular marijuana users, a new study suggests.

After reviewing the medical records of 250 Colorado patients who got colonoscopies and other endoscopic procedures, researchers determined that regular marijuana users needed more anesthesia than those who didn’t use cannabis, according to the study published in the Journal of the American Osteopathic Association. In fact, marijuana users needed more than twice the amount of propofol, a powerful anesthetic, compared to others, the researchers found.

“Although marijuana use has been legalized for recreational and medical use in many states, it’s been a very poorly studied substance,” said the study’s lead author, Dr. Mark Twardowski, a specialist in internal medicine who is in private practice in Colorado. “So we can’t say it doesn’t have an effect on other medications and substances that patients might be using. Our study demonstrates that it seems to have an effect on at least the classes of medication used for sedation for simple endoscopic procedures.”


storyline Daily use of powerful pot linked to severe mental disorders, European study finds

Twardowski typically starts with a low dose of the sedating medications and increases the amount until the patient is relaxed, but awake, and is comfortable during the procedure.

“Usually you know you need more if the patient tells you they’re feeling uncomfortable or you notice them starting to grimace or start shifting around on the table,” he explained.

“Knowing if someone is using marijuana regularly might affect how we do anesthesia.

Twardowski got the idea for his study after noticing that marijuana users seemed to require higher levels of sedation, he said. He and his colleagues reviewed files on patients who had gotten endoscopic procedures between January 1, 2016 and December 31, 2017 — a period when cannabis was legal — at an endoscopy center located in the surgical services department at a Level III trauma hospital in a small Colorado city.

Out of the 250 patients examined in the study, 25 were regular cannabis users. When the researchers compared the records of the 25 to those from non-users they found increased levels of all three sedatives had been needed to achieve the right level of anesthesia. Compared to non-users, regular marijuana users required:

  • 14 percent more fentanyl
  • 19.6 percent more midazolam
  • 220.5 percent more propofol

Twardowski said his findings underscore the importance of patients telling their surgeons about marijuana use.

“Knowing if someone is using marijuana regularly might affect how we do anesthesia,” he explained.

Marijuana-related ER visits spike at Colorado hospital after legalization

The fear, Twardowski said, is that increasing those medications might end up “pushing high the danger of shutting off a patient’s respiration — while still not achieving pain control.”

The new findings weren’t a surprise to Dr. Ajay Wasan, a professor of anesthesia and psychiatry at the University of Pittsburgh School of Medicine and vice chair for pain medicine in the department of anesthesia at the University of Pittsburgh Medical Center.

“Any kind of brain-altering substance can have an effect on another brain-altering drug,” Wasan said.

While the new study includes just 25 cannabis users, “it’s completely consistent with other small similar previous studies,” Wasan said after reading the research. “All together they suggest long-term marijuana use has an impact on anesthesia care.”

Studies like this one add to the growing evidence of emerging health problems that recreational marijuana use can have, Wasan said.

“We’re getting all these signals from different parts of the health care system. One important message is that we have to use California and Colorado as learning labs,” he said.

Because cannabis was designated by the DEA as a Schedule 1 drug alongside substances such as LSD, heroin and MDMA, researchers have not had the opportunity to fully investigate marijuana. There’s no question that there needs to be more research on cannabis, said Dr. Anthony Watkins, an assistant professor of surgery at Weill Cornell Medicine and an abdominal transplant surgeon at NewYork-Presbyterian/Weill Cornell Medical Center.

“We do know that there are some drugs that are commonly prescribed to patients that marijuana can either decrease or increase the breakdown of,” Watkins said.

Linda Carroll is a regular health contributor to NBC News and Reuters Health. She is coauthor of “The Concussion Crisis: Anatomy of a Silent Epidemic” and “Out of the Clouds: The Unlikely Horseman and the Unwanted Colt Who Conquered the Sport of Kings.”

Does marijuana affect anesthesia? People who regularly use weed may need higher levels of sedation, a new study suggests.