Cannabis Use and Mental Health Disorders

This post discusses current and past research linking the use of cannabis with an increased risk of anxiety, paranoia, violent behavior, depression, bipolar disorder and schizophrenia.

The use of cannabis has been increasing worldwide and substantial research shows that its use is linked to increased risk of psychiatric disorders.

Cannabis has been legal in the Netherlands in coffee shops since 1976. The Canadian government legalized cannabis in 2018. As of April 2023, cannabis is legal for medical use in 38 states, three territories, and in the District of Columbia.[i] Medical marijuana is becoming more available in Europe but cannabis remains illegal in most EU countries for personal use.

Cannabis refers to the plant, while marijuana refers to the dried flowers, leaves, stems and seeds of the cannabis plant.

CBD is the non-psychoactive chemical compound found in cannabis. It does not make people high. THC found in cannabis is the psychoactive part of marijuana. It makes people high.

In 1845, psychiatrist Dr. Moreau published a book called Hashish and Mental Illness in which he noted in great detail the similarities between psychosis and ingesting high doses [of cannabis].

Messing with Heads documentary, published July 2005

The link between cannabis use and mental health disorders has been known for years. The following are excerpts from the documentary “Messing with Heads”:

“Sydney psychiatrist DR ANDREW CAMPBELL: My view is that it [cannabis] is bringing on new cases of psychosis. … I see a lot of people with long standing psychosis and if I see 10 people in a day, seven of them will have used cannabis on a daily basis at the first time of onset of psychosis.

JANINE COHEN: … The large study found exposure to cannabis during adolescence and young adulthood increased the risk of psychotic symptoms later in life …. The more they smoked, the greater the risk of further symptoms – hallucinations and hearing voices. The risks increased fourfold for those who were already vulnerable to psychotic symptoms.

DR. ANDREW CAMPBELL: … Where people are counting, the evidence is now coming out that there is an increasing risk of psychosis in increasing rates – particularly in young men. That’s coming out of the Netherlands, its coming out of Italy, there are some reports, I’ve heard about anecdotally from America, which has the same problem.

PROFESSOR WAYNE HALL, INSTITUTE FOR MOLECULAR BIO-SCIENCE, QLD UNIVERSITY: But certainly, there are enough case histories in the literature of individuals who had no preceding history of psychosis before the cannabis use, who did develop marked psychotic symptoms with very high does of cannabis – often given for medicinal or other reasons. So it is possible that it could produce psychotic illness in people without vulnerability.

PROFESSOR PAT MCGORRY, EPPIC: Well, the outcome can be death. I mean 10 to 15 per cent of young people with a serious mental illness will die in the early years after diagnosis from suicide and other causes, so this is a potentially lethal situation. The scenario in terms of wasted lives is much more pervasive, I suppose. We can get 90 per cent of our young people symptom free with treatment, even with severe psychosis, but only 50 per cent of them are going to go back to meaningful vocational activity.

Watch Messing with Heads documentary here

Cannabis use linked with depression and bipolar disorder

The study, Cannabis Use Disorder and Subsequent Risk of Psychotic and Nonpsychotic Unipolar Depression and Bipolar Disorder, analyzed over 6 million people in Denmark and found that cannabis use disorder was associated with an increased risk of depression and bipolar disorder in this large cohort group.

Another study examined the health records of 6.9 million people and determined that up to 30 percent of schizophrenia diagnoses could have been prevented if men from 21 to 30 years old had not developed cannabis use disorder.

Cannabis use is also associated with higher odds of depression and depression severity in adolescence. Researchers stated that depression and cannabis use are independently associated with higher odds of suicide attempt.[ii]

Cannabis use disorder

Cannabis use disorders (CUDs) are usually associated with dependence and when someone stops taking cannabis, they will experience withdrawal symptoms.

“People who use marijuana often report irritability, mood and sleep difficulties, decreased appetite, cravings, restlessness, and/or various forms of physical discomfort that peak within the first week after quitting and last up to two weeks,” explains Nora Volkow, MD, director of the National Institute on Drug Abuse (NIDA).[iii]

The significant increase in the concentration of THC in cannabis may also be responsible for cannabis use disorder.

“The potency of cannabis products [in the past] used to be much weaker, perhaps contributing to the impression that marijuana is not addictive,” explains Deborah Hasin, Ph.D., professor of epidemiology at Columbia University in New York City. “However, potency has increased greatly over the last few decades. Updated figures show that 20 to 30% of cannabis users develop CUD, so the risk for addiction is real.” This is why Dr. Hasin feels that marijuana consumption of any amount can be a concern.

Cannabis use and violence

The study, Continuity of cannabis use and violent offending over the life course, found that continued cannabis use is associated with a 7-fold greater risk for committing violent crimes.

Marijuana and Schizophrenia

The 2023 study, Association between cannabis use disorder and schizophrenia stronger in young males than in females, reported that young males might be particularly susceptible to the effects of cannabis on schizophrenia.

Marijuana use has also been linked to depression, social anxiety, and thoughts of suicide, suicide attempts, and suicide.[iv]

What areas of the brain are affected by marijuana use?

The CDC website states that the use of marijuana directly affects brain function with respect to areas of the brain responsible for memory, learning, attention, decision-making, coordination, emotions, and reaction time.

Within 24 hours of marijuana use, youth and adults have an immediate impact on thinking, attention, memory, coordination, movement, and time perception.1

 The brain does not become fully developed until the mid-to-late 20s. Thus, regular marijuana use in teens and young adults can have a long-term impact on brain development.

The impact of marijuana use on the brain depends on many factors, including:

  • amount of THC and its strength
  • how often cannabis is used
  • the age of the person when first used
  • if other substances like tobacco and alcohol are used at the same time.[v]

Marijuana use, especially if used frequently (daily or nearly daily) and in high doses, can cause disorientation and sometimes cause feelings of anxiety and paranoia.1

People who use marijuana regularly are more likely to develop temporary psychosis (hallucinations and paranoia) and long-lasting mental disorders like schizophrenia (where people see or hear things that are not present).2

The association between marijuana and schizophrenia is stronger in people who start using marijuana at an earlier age and use marijuana more frequently.

Marijuana disrupts sleep

THC is often taken to promote sleep – to speed up the time in which you fall asleep.

It blocks REM sleep in the middle of the night causing the brain to become starved of REM sleep. Then, when a person stops using THC, the brain tries to get back the REM sleep and can cause them to have crazy dreams.

Unfortunately, the brain is never able to fully get back the REM sleep. With THC, a person builds up a debt for REM sleep. There is a rebound mechanism from using THC.

A big problem with the use of THC is withdrawal and dependency.

When a person starts to use THC for sleep, there can be added dependency and tolerance. In time, they will need more THC to have the same sleep benefit.

And when they stop using it, they will usually get a severe rebound of insomnia. This can be so potent that it is part of the clinical withdrawal profile from THC. You can also experience anxiety from the withdrawal.

Many believe that they’re not addicted because they don’t follow the usual profile of a classic addiction. But they will experience intense anxiety without marijuana when it is taken away. This speaks to a dependency.

A significant amount of past research and a growing body of current research warns of the risks of regular cannabis use. The THC in cannabis impacts brain function and is linked with an increased risk of many mental health disorders. It is important to weigh the benefits versus potential adverse effects of any given treatment. It is also important to pick a therapy that will not cause more harm than good. By treating the root cause of pain, insomnia and anxiety, we will not have to rely on treatments like cannabis that have the potential to greatly impact our mental health, relationships and quality of life.

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