Health effects of cannabis

Health effects

of cannabis

There are both potential therapeutic uses for and potential

health risks of using cannabis (marijuana). A chemical called

delta-9-tetrahydrocannabinol (THC) is responsible for the way

your brain and body respond to cannabis. While it is used by

some for therapeutic purposes, there are short- and long-term

physical and mental health effects that can be harmful.

Short-term health effects

While cannabis may make you feel relaxed and happy,

you could experience unpleasant, unwanted or negative

effects on your brain and body.

Effects on the brain

The short-term effects of cannabis on the brain can include:

f confusion

f sleepiness (fatigue)

f impaired ability to:

f remember

f concentrate

f pay attention

f anxiety, fear or panic

f reduced ability to react quickly

Cannabis use can also result in psychotic episodes

characterized by:

f paranoia

f delusions

f hallucinations

Emerging evidence suggests that a chemical in cannabis

called cannabidiol (CBD) may help dampen some of the

psychoactive effects of THC

such as:

Bhattacharyya et al. (2010) Opposite effects of delta-9-

tetrahydrocannabinol and cannabidiol on human brain function

and psychopathology. Neuropsychopharmacology 35(3): 764–74.

www.ncbi.nlm.nih.gov/pubmed/23550724

f disturbances in mood

f psychotic symptoms

There is also evidence to suggest that combining tobacco

with cannabis can increase:

f the strength of some psychoactive effects

f the risk of poor mental health outcomes,

including dependence

Effects can be felt within seconds to minutes of smoking,

vaporizing or dabbing cannabis. These effects can last up

to 6 hours or longer.

If you eat or drink cannabis, these effects can occur within

30 minutes to 2 hours and can last up to 12 hours or longer.

Effects on the body

The short-term effects of cannabis on the body can include:

f damaged blood vessels caused by the smoke

f decreased blood pressure, which can cause people

to faintor pass out

f increased heart rate, which can be a danger for people

with heart conditions and can lead to an increased risk

ofheart attack

Ramo et al. (2015) Tobacco and marijuana use among adolescents and

young adults: a systematic review of their co-use. Clinical Psychology

Review 32: 105–121. www.ncbi.nlm.nih.gov/pubmed/22245559

Schauer et al. (2017) Marijuana and tobacco co-administration in blunts,

spliffs, and mulled cigarettes: a systematic literature review. Addictive

behaviors. 64: 2011–211. www.ncbi.nlm.nih.gov/pubmed/27654966

Wang et al. (2016) One minute of marijuana secondhand smoke

exposure substantially impairs vascular endothelial function.

Journal of the American Heart Association. 5(8).

www.ncbi.nlm.nih.gov/pubmed/?term=27464788

Thomas et al. (2014) Adverse cardiovascular, cerebrovascular, and

peripheral vascular effects of marijuana inhalation: what cardiologists

need to know. American Journal of Cardiology 113(1): 187–90.

www.ncbi.nlm.nih.gov/pubmed/24176069

HEALTH EFFECTS OF CANNABIS2

Impairment

The THC in cannabis can impair your ability to drive safely

and operate equipment. It can also increase the risk of falls

and other accidents. This is because THC can affect your:

f coordination

f reaction time

f ability to pay attention

f decision-making abilities

f ability to judge distances

Cannabis use can increase the risk of accidents that lead to

injury or death during higher-speed activities, such as driving,

biking or skiing.

Impairment can last for more than 24 hours after cannabis

use,

well after other effects have faded.

People who use cannabis regularly may have trouble with

certain skills needed to drive safely

for weeks after their

lastuse.

Combining alcohol with cannabis greatly increases the level

of impairment and the risk of injury or death from accidents.

Combining cannabis with other psychoactive substances,

especially ones that have sedative effects, such as opioids

and benzodiazepines, can increase the effects of the drugs.

This could increase the risk of injury or harm, particularly

with activities like driving.

Long-term effects

Long-term effects develop gradually over time with frequent

use (daily or near-daily) that continues over weeks, months

oryears. These effects can last from several days to months

orlonger

after you stop using cannabis.

Leirer, V. O. et al. (1991) Marijuana carry-over effects on aircraft

pilot performance. Aviat. Space Environ. Med. 62, 221–227.

www.ncbi.nlm.nih.gov/pubmed/1849400

Karschner et al. (2016) Extended plasma cannabinoid excretion

in chronic frequent cannabis smokers during sustained abstinence

and correlation with psychomotor performance. Drug Testing and

Analysis 8(7): 682–9. www.ncbi.nlm.nih.gov/pubmed/26097154

8,9

Meier et al. (2012) Persistent cannabis users show neuropsychological

decline from childhood to midlife. Proceedings of the National

Academy of Sciences USA 109(40): E2657–64.

www.ncbi.nlm.nih.gov/pubmed/22927402

Effects on the brain

The long-term effects of cannabis on the brain can include

an increased risk of addiction and harm to your:

f memory

f concentration

f intelligence (IQ)

f ability to think and make decisions

These effects appear to be worse for youth who start

using early, and who use cannabis frequently and over a

long period of time. They may not be fully reversible when

cannabis use stops.

Effects on the body

Some of the long-term effects of smoking cannabis on

the body are similar to the effects of smoking tobacco

and can include risks to lung health, including:

f bronchitis

f lung infections

f chronic (long-term) cough

f increased mucus buildup in the throat

Potential therapeutic uses

There is some evidence of potential therapeutic uses of

cannabis or its component chemicals (cannabinoids).

Health Canada provides information for health care

professionalsand for authorized patients on the use of

cannabisand cannabinoids for medical purposes. This includes

information on dosing, adverse effects, warnings and more.

Risks of illegal cannabis

There may be other health and safety risks associated with

cannabis obtained illegally. For example, the THC potency of

illegal cannabis is often unknown, so you could end up using a

stronger product than expected. This could heighten or prolong

effects such as confusion or anxiety.

The quality and purity of illegal cannabis cannot be guaranteed

and is frequently mixed with or contains:

f pesticides

f other drugs

f heavy metals

f moulds or fungi

f other contaminants

HEALTH EFFECTS OF CANNABIS

Cat.: H129-73/2017E (Print)

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H129-73/2017E-PDF | ISBN: 978-0-660-08291-2 (Print)

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978-0-660-08290-5 (PDF) | Pub.: 170012

There is also the serious risk of:

f interacting with criminals or criminal organizations

f criminal charge and prosecution

Mental health effects

In some people, cannabis use increases the risk of developing

mental illnesses like psychosis or schizophrenia, especially

in those who:

f start using cannabis at a young age

f use cannabis frequently (daily or almost every day)

f have a personal or family history of psychosis

and/or schizophrenia

Frequent cannabis use has also been associated with

an increased risk of:

f suicide

f depression

f anxiety disorders

Health effects on youth

Cannabis use that begins early in adolescence, that is

frequent and that continues over time has been associated

with increased risk of harms. Some of those harms may

not befully reversible.

Adolescence is a critical time for brain development,

as research shows the brain is not fully developed until

around age 25.

Youth are especially vulnerable to the effects of cannabis

on brain development and function. This is because THC

in cannabis affects the same biological system in the

brain that directs brain development.

It is important for parents, teachers, coaches and other

trusted adults to be ready to talk with youth about drugs.

Volkow et al. (2016) Effects of cannabis use on human behavior,

including cognition, motivation and psychosis: a review. JAMA Psychiatry

73(3): 292–7. www.ncbi.nlm.nih.gov/pubmed/26842658

Health effects on pregnancy

and children

Just like with tobacco, a pregnant woman or new mother’s

use of cannabis can affect her fetus or newborn child

which can lead to health problems.

The toxins in cannabis are carried through the mother’s

blood to her fetus during pregnancy and in the breast milk

following birth.

Heavy cannabis use during pregnancy can lead to lower

birth weight of the baby. It has also been associated

with longer-term developmental effects in children

and adolescents, such as:

f decreases in:

f memory function

f the ability to pay attention

f reasoning and problem-solving skills

f hyperactive behaviour

f increased risk for future substance use

Addiction

Contrary to popular belief, people can become addicted to

cannabis. Individuals who use cannabis can develop a cannabis

use disorder, which at its extreme can result in addiction.

Continued, frequent and heavy cannabis use can cause

physical dependency and addiction.

Research has shown that THC in cannabis causes an increase

in levels of dopamine, the pleasure chemical, in the brain.

This motivates people to keep using it.

Addiction can develop at any age but youth are especially

vulnerable

as their brains are still developing.

Some people are also more prone to becoming addicted

than others. It’s estimated that 1 in 11 (9%) cannabis users

will develop an addiction

to it. This statistic risesto about 1

in 6 (17%) for people who started using cannabis as a teenager.

If a person smokes cannabis daily, therisk of addiction is

25% to 50%.

Chadwick et al. (2013) Cannabis use during adolescent development:

susceptibility to psychiatric illness. Frontiers in Psychiatry. 4: 129.

www.ncbi.nlm.nih.gov/pubmed/24133461

Volkow et al. (2014) Adverse health effects of marijuana use.

New England Journal of Medicine 370(23): 2219–27.

www.ncbi.nlm.nih.gov/pubmed/24897085

HEALTH EFFECTS OF CANNABIS

Problematic cannabis use can include some or all of the

following behaviours:

f failing to fulfill major duties at work, school or home

f giving up important social, occupational or recreational

activities because of cannabis use

f consuming it often and in larger amounts or over a longer

period than they intended

f being unable to cut down on or control cannabis use

People who display most or all of these behaviours over a

12-month period may have cannabis addiction.

Some people can develop a tolerance to the effects of

cannabis. Tolerance is characterized by a need for a larger

dose of a drug to maintain the original effects. Tolerance to

some of the effects of cannabis can develop after a few doses.

In some people, tolerance can eventually lead to physical

dependence and/or addiction.

Addiction help

Cannabis addiction can cause serious harm to your health,

social life, school, work and financial future.

If you or someone you know is struggling with addiction

tocannabis or other drugs, help is available.