Does dope smoking damage your health?

It won't kill you, but just what are the effects of cannabis? Some answers from the latest research.


How toxic is cannabis?


No one has died as a direct and immediate consequence of recreational or medical use, although the British House of Lords survey reports five cases of death from inhalation of vomit after cannabis use in the mid-1990s.

Animal tests suggest that a fatal overdose would take 40,000 times the amount needed to get stoned.


Can it affect your heart?


Marijuana can cause a significant increase in heart rate of 20 to 50 per cent over baseline. This occurs within 15 minutes and lasts up to three hours.

Blood pressure also changes. Healthy young hearts will only be mildly stressed, but patients with angina or other cardiovascular diseases may be at risk.


What does it do to your lungs?


Most pot-smokers also smoke cigarettes, so isolating the effects of one or the other can be difficult.

The expert is University of California lung specialist Donald Tashkin, who for 17 years has monitored the respiratory system of more than 130 regular marijuana smokers, comparing them with others who smoke just tobacco, marijuana and tobacco, or nothing at all.

His conclusion: puff for puff, marijuana is harder on the lungs than tobacco.

"Smokers of marijuana had as frequent symptoms of chronic bronchitis as smokers of tobacco, despite the fact that the tobacco smokers smoked more than 20 cigarettes a day, compared with the three to five joints a day used by marijuana smokers."

There were similar levels of cell damage in the lungs and of abnormalities in cell nuclei, and changes in genes known to have an early role in cancer development.

The explanation is simple: joints yield up to three times more tar than cigarettes because they are loosely packed and unfiltered. Marijuana smokers inhale more deeply and hold their breath four times as long, resulting in tar deposits 40 per cent higher.

Tashkin also argues that marijuana smoke is richer in carcinogens, though that is disputed by other researchers.

So does smoking marijuana cause cancer? It is too soon to tell. Tashkin says the marijuana epidemic began in the late 1960s and the bulk of smokers are just now reaching the age of 50.


Can you smoke and drive?


Cannabis affects users' coordination and short-term memory, impairing their ability to perform skilled tasks such as driving and using machinery. The impairment is dose-related and temporary.

There is disagreement about how long impairment lasts. Most assume only a few hours, but one British researcher claims it can persist for up to 48 hours.

The research suggests that driving impairment is not severe, perhaps because stoned drivers compensate by taking fewer risks and driving more slowly, whereas alcohol tends to encourage risk-taking and aggression.

However, if something unexpected happens, the stoned driver's ability to respond is affected.


Are there long-term effects on the brain?


Daily users, after several days of abstinence, continue to show subtle but measurable cognitive impairments. But this could be the result of slow release of marijuana constituents stored in the brain and fatty tissues.

A World Health Organisation report says a 1971 paper suggesting that chronic heavy use may cause gross structural brain damage was flawed. Subsequent studies have failed to find any evidence.

University of Texas researchers have spent 25 years testing the mental skills of heavy users in Costa Rica. Although some had smoked 10 joints a day for over 30 years, their ability to learn and remember lists of words was only mildly impaired.

Researchers at Johns Hopkins University, Baltimore, surveyed 1300 people aged under 65 three times between 1981 and 1996. There was no significant difference in cognitive decline between heavy users, light users and non-users.


Is it addictive?


It is uncertain whether marijuana produces withdrawal symptoms the way heroin, cocaine, alcohol and nicotine do. The most researchers have been able to discern is occasional cases of mild and short-lived anxiety and insomnia upon abrupt cessation after years of heavy use.


Are teenagers particularly vulnerable?


Links are often made between marijuana use and poor school performance, minor delinquency, lack of ambition and antisocial behaviour.

Studies in Christchurch and the United States suggest that youngsters who move from experimental use to problem use tend to come from disadvantaged or dysfunctional families.

Once caught up in the drug culture, they are encouraged to adopt other antisocial behaviour, leading to poor educational attainment, offending and poor job prospects.


Is marijuana the gateway to hard drugs such as heroin?


There is no causal link. About 95 per cent of marijuana users will not use hard drugs. The US Institute of Medicine says the "gateway drugs" for most hard drug users are alcohol and nicotine.


Can cannabis trigger mental illness?


Heavy cannabis use is linked with the onset and worsening of schizophrenia and other psychotic disorders in people predisposed to these illnesses.


Does marijuana have therapeutic benefits?


In November 1998, the House of Lords supported a law change to permit the use of cannabis to relieve pain and multiple sclerosis.

Positive results have been reported in treating the painful muscle spasms and tremors that MS sufferers are prone to, and in aiding bladder control.

However, the Lords did wonder whether "the beneficial effects ... might simply be related to the wellbeing caused by the intoxicant properties of the drug."

Trials in the 1970s showed cannabis-derived drugs were an effective anti-emetic, particularly for people undergoing chemotherapy.

It is argued that the "munchies" experienced after cannabis use help anorexics to eat. In the United States, THC, a component of cannabis, has been licensed for treating anorexia associated with Aids. It reduces nausea, prevents further weight loss and improves the patient's mood.

Glaucoma researchers have lost interest in using marijuana to reduce intraocular pressure. To work, it must be taken every two to four hours, and patents did not like being continuously high.