Health risks of cannabis use

Knowledge about cannabis and its impacts is constantly evolving. Various factors seem to contribute to negative effects in some people.

Although problems may occur for first-time cannabis users, issues related to physical and mental health mainly arise as a result of repeated use over several months or years. Accidents and injuries, on the other hand, may occur as a result of one-time or occasional use. Certain factors can increase or reduce a cannabis user’s risk of being negatively affected:

• A personal or family history of mental health issues such as psychosis and bipolar disorder
• Frequency of use: Regular use (once a week or more) is often linked to increased risk of health problems
• Type of product used: Products with higher THC content may be more harmful
• The age at which a person starts to use cannabis: use during adolescence is generally associated with an increased risk of negative effects
• The circumstances of use, for example:
  • When cannabis is combined with other substances such as alcohol or medications
  • When an individual has personal responsibilities such as work or the supervision of children
• The method of use: Smoking cannabis appears to be more risky than other methods of use, although poisoning from foods containing cannabis is common among inexperienced users. For more information, visit the Risks associated with methods of cannabis use page.

However, caution should be exercised before attributing the cause of a health problem to cannabis use. It is possible that the problem:

• Was already present prior to cannabis use
• Is a result of cannabis use
• Is influenced by cannabis use or, conversely, influences cannabis use

Based on these factors, it is difficult to predict whether or not an individual will experience significant problems after using cannabis. Most experts agree that cannabis use is never 100% safe.

The health risks and negative health impacts of cannabis use stem from its effects on cognitive abilities, such as:

• Judgement
• Attention span
• Memory
• The ability to make decisions

These effects can impact daily activities such as:

• Driving a car
• Work
• Learning activities
• Other situations that require coordination and speed

Cannabis begins to take effect within minutes of being inhaled, and a little later if ingested. The effects often last for several hours and are usually reversible. Some studies suggest that reduced cognitive function may persist longer in the event of sustained and repeated use, especially if it begins in adolescence.

Cannabis use can exacerbate some existing health problems, such as chronic diseases:

• Cannabis use increases the heart rate and can alter its rhythm. It also increases blood pressure.
• Inhaling cannabis smoke can aggravate existing respiratory diseases and even promote disease onset.
• Like tobacco smoke, cannabis smoke contains a number of substances that are harmful to your health, including some carcinogens.
• However, the most recent scientific studies do not prove that the risk of developing lung, throat, or neck cancer is higher among cannabis users.

Also, cannabis vaping is associated with a risk of developing an acute lung disease. This practice should be avoided. To learn more about the risks associated with vaping cannabis, see the warning against vaping cannabis  (in French only) on the website of the Ministère de la Santé et des Services sociaux.

Psychotic symptoms

Individuals who are under the influence of cannabis may experience psychotic symptoms such as:

• Hallucinations with false visual, auditory, and/or tactile perceptions
• Paranoid ideas that seem detached from reality

In most cases, these psychotic experiences are limited to when the person is intoxicated and disappear on their own. Other individuals may experience persistent, long-term, and much more serious symptoms. According to experts, cannabis use does not cause psychotic disorders, but it can be a contributing factor for some people.

Symptoms of depression

Individuals who regularly use cannabis may show a lack of interest in activities other than using cannabis (studies, work, leisure, etc.). They may also experience symptoms of depression, for example:

• Deep sadness
• Fatigue
• Irritability
• Sense of worthlessness

Some individuals with depression may be tempted to use cannabis to relieve their symptoms. To date, scientific evidence has not shown that cannabis is effective in treating depression. Using it for this purpose is not recommended.

Anxiety

Some studies suggest that cannabis users experience symptoms of anxiety more frequently than non-users. However, it is difficult to predict whether or not cannabis will influence their anxiety levels. Some people may experience panic attacks when they use cannabis, while others find it relaxing.

Problematic cannabis use

Cannabis use can be problematic if people lose control of their use and suffer negative consequences in various spheres of their life as a result. Some people may become addicted to cannabis, as it is the case with other substances. Individuals may:

• Develop a tolerance to the substance (i.e., need to use more to feel the same effect)
• Experience withdrawal symptoms when they reduce or stop use
• Have a strong desire to use
• Be unable to stop using
• Spend a significant portion of their time buying or using cannabis or recovering from cannabis use
• Use repeatedly in such a way that it prevents them from fulfilling important obligations at work, school, or home
• Use despite personal and/or social problems related to use
• Reduce or give up social, professional, or leisure activities as a result of use

About 1 in 11 people who use cannabis will develop a problematic use of cannabis in their lifetime. Among adolescents, 1 in 6 users will develop addiction problematic use. Use of and addiction to other products including alcohol and tobacco are more common among cannabis users.

Research has also established the existence of a cannabis withdrawal syndrome. It occurs when regular cannabis users significantly reduce or stop cannabis use. Symptoms include:

• Restlessness
• Irritability
• Sleep problems, which may last a number of weeks after stopping use

The health risks of cannabis use increase with both the frequency (e.g., number of times used in a week) and duration of use (e.g., number of years used).

Cannabis and alcohol

Whenever you drink alcohol or take a drug, the effect the substance will have on you is always a bit unknown. Mixing alcohol with recreational or prescription drugs increases the likelihood of harmful effects . That’s why a lot of cannabis users drink little or no alcohol when they consume cannabis. They know the two don’t mix.

Mixing cannabis with alcohol further reduces your ability to drive a vehicle.

Cannabis and tobacco

Mixing cannabis and tobacco isn’t a good idea either. Their combined use presents a greater health risk—not to mention that tobacco is highly addictive.

Drug interactions

Cannabis can have an impact on the effect of the medication you’re taking. The inverse is also true: some medications can alter the effects of cannabis. Before consuming cannabis, ask a health professional if there are any known interactions with your medications.

When a mother consumes cannabis, the THC winds up in the placenta she’s carrying and in her breast milk. Since the short- and long-term effects of THC exposure on fetuses and babies are currently unknown, it’s best to avoid cannabis and cannabis-derived products and exposure to secondhand smoke if you’re pregnant or breastfeeding. If you’re having a hard time giving up cannabis, talk to a trusted health professional.

For more information, visit the Alcohol or other drug use during pregnancy and breastfeeding page.

As with alcohol, drivers must not get behind the wheel if they have used cannabis because its effects on the brain can impair their ability to drive.

The effects of cannabis vary according to a number of factors and can last for several hours after consumption. Cannabis severely affects our perceptual and psychomotor functions, which are essential for driving. For example, drivers whose faculties are impaired due to cannabis may have:

• Difficulty concentrating and staying focused on the road environment (e.g., failing to obey road signs)
• Longer reaction times and slower reflexes (e.g., taking longer to brake)
• A reduced ability to properly assess their surroundings
• Difficulty maintaining a straight course
• Coordination problems
• Impaired judgement

People who drive under the influence of cannabis are almost twice as likely to have an accident as those who have not used the drug. Drivers who consume alcohol and cannabis together have a much higher risk of causing an accident.

To learn more about the risks of cannabis use and driving, visit the Société de l’assurance automobile du Québec (SAAQ)  website.