How cannabis affects your health [PDF: 426.24 KB]
Introduction
Cannabis is the most widely used illicit drug in Australia . One in every three Australians (aged 14 years and over) has used cannabis at some time in their lives. Although most cannabis use is experimental or infrequent, it has been estimated that approximately one in 10 people who try it become dependent.
The most common way of using cannabis in Australia is smoking the heads and leaf of the plant. However, it has also been used in cakes or biscuits. The active chemical in cannabis is delta-9 tetrahydrocannabinol (THC). When cannabis is used, THC is absorbed into the bloodstream and carried to the brain, producing the "high" feeling. Inhaled THC gets into the bloodstream quicker than THC that is eaten. This means that the effects of cannabis when smoked (inhaled) occur more rapidly.
This fact sheet outlines some of the ways in which cannabis use affects your health. The specific effects vary from person to person and depend on the drug itself and the conditions under which it is used.
Is cannabis harmful?
Cannabis use causes intoxication, which includes a range of psychological and physical changes in the body. It can be harmful in a number of ways, through immediate effects and damage to health over time.
Short-term effects — small doses
Small quantities of cannabis can have effects that last 2-4 hours after smoking. These effects include:
- relaxation and loss of inhibition
- increased appetite
- enhanced sensory perception — distorted sense of judgement, time and space
- thinking and short-term memory problems
- impaired coordination and balance
- 20-50 per cent increase in heart rate
- low blood pressure
- faintness
- reddened eyes.
Short-term effects — large doses
Larger quantities of cannabis make the above effects stronger, and also tend to distort a person's perceptions. For example, very large quantities of cannabis can cause:
- confusion
- restlessness
- feelings of excitement
- hallucinations
- anxiety or panic, or detachment from reality
- decreased reaction time
- paranoia.
Investigations of the short-term negative health effects of cannabis have primarily focused on the role of the drug in triggering heart attack or aggravating the symptoms of a pre-existing heart condition. There is also concern that cannabis use can trigger psychosis in vulnerable individuals (see Fact Sheet No. 3.14, Cannabis use and mental health: the facts).
There have been no documented cases of death from cannabis overdose; however, some of the physical effects related to cannabis use, such as "cannabis psychosis" and distorted judgement, can place people at risk of injury.
Long-term effects
Most of the negative health consequences associated with cannabis use result from heavy use over the long-term. Research in Australia and the United States of America shows evidence of some long-term effects in some regular cannabis users.
Respiratory illness
The way that cannabis is smoked means that more tar is inhaled and retained in the lungs than tobacco, placing cannabis users at an increased risk of respiratory illness. Cannabis smoke causes respiratory inflammation even in relatively young people who smoke cannabis regularly. Someone who smokes cannabis regularly may have many of the same respiratory problems that tobacco smokers do, such as:
- persistent cough and increased phlegm production
- a higher risk of lung infections
- a greater chance of experiencing obstructed airways.
Cancer
Cannabis smoke is carcinogenic and causes mutations in cells, raising the risks of cancer development in the areas of the body that are exposed to cannabis smoke. Cannabis use has been associated with cancer of the tongue, neck, lung and upper respiratory tract. Cannabis smoke contains 50–70 per cent more cancer-causing ingredients than tobacco smoke. The risk is also increased by the tendency of cannabis users to inhale more deeply and hold their breath longer than tobacco smokers, which increases the lungs' exposure to carcinogenic smoke.
Impaired immune system
There has been concern that cannabis smoke, like tobacco smoke, may impair the functioning of the immune system. It is thought that THC impairs the immune system's ability to fight off infectious diseases and cancer.
Changes to hormone production
Cannabis can affect hormone production. Research shows that some cannabis users have a reduced sex drive. Cannabis can also affect fertility by reducing the sperm count in men and inhibiting ovulation in women.
Human studies also suggest that cannabis use affects embryo implantation and may cause miscarriage.
Impaired brain functioning
Concentration, memory and the ability to learn can all be reduced by regular cannabis use. The damage to short-term memory seems to occur because THC alters the way in which information is processed by the hippocampus, a brain area responsible for memory formation. These effects can last for several months after cannabis use is stopped.
Decrease in IQ
Overall, there is some evidence indicating that heavy current cannabis use is associated with a moderate decrease in IQ. However, these effects do not appear to persist once cannabis use has ceased for some months. There is evidence that those who start to use cannabis at a young age are more likely to have reduced verbal abilities. However, it is unknown whether this is due to social factors or the actions of cannabis in the brain. Nevertheless, cannabis use is associated with impaired educational outcomes, delinquency and crime.
Disturbed sleep patterns
In some cases sleep patterns are disrupted by cannabis use. Some people may need to use cannabis to get to sleep while others may find it hard to get to sleep after using cannabis.
Tolerance and dependence
Cannabis is physically addictive. The brain cells that are affected by THC adapt to the drug over time and greater amounts are required to achieve the same effect. As a result, the body builds up a tolerance to cannabis and withdrawal symptoms occur if the drug is stopped.
Medical uses of cannabis
Some cannabis users report that cannabis helps relieve the symptoms of medical problems. It has been reported that cannabis may be useful for the following conditions:
- pain relief, for example, in people with cancer
- relief of nausea and vomiting, particularly in people having chemotherapy
- reduction of wasting or severe weight loss, in people with cancer or AIDS, by increasing their appetite and relieving nausea
- relief of symptoms of some neurological disorders; for example, muscle spasms caused by multiple sclerosis, spinal cord injury and other movement disorders
- one of the short-term effects of the THC in cannabis is to expand the airways in the lungs, which helps people who have asthma; however, this may stop after a person has developed a tolerance for the drug and also exposes the person to lung disease through the carcinogens in smoke and cannabis.
Getting help
Long-term, heavy cannabis use is associated with some serious health problems. If you feel that your cannabis use is problematic help is available:
- DirectLine, tel. 1800 888 236
Confidential counselling and referral, 24 hours, 7 days
- Youth Substance Abuse Service, tel. 1800 014 446
24-hour counselling, support and referral for 12-21-year-olds
- Family Drug Help, tel. 1300 660 068
A support service staffed by trained volunteers and professional counsellors
For more information on drugs and drug prevention contact the DrugInfo Clearinghouse on tel. 1300 85 85 84 , email druginfo@adf.org.au, or see our website www.druginfo.adf.org.au.