Cannabis and the risks: facts you need to know
I used to have fairly liberal views on cannabis and have compared it favourably in the past with alcohol and tobacco, both of which exact a bigger toll on our society than all illegal drugs combined. But, along with most doctors, I have become increasingly concerned in recent years that the drug is much more dangerous than we thought, and certainly nowhere near as safe as most teenagers still think.
The days are gone when sensible people argue that cannabis is harmless. The evidence that has been collected over the past decade shows that it is clearly not, although for most of the 3-4 million people in the UK who dabble the risks are still small. The vast majority are occasional users who, with time, will eventually turn their backs on the drug and emerge unscathed. This is in stark contrast to the outlook for the tens of millions who use cigarettes and alcohol - two legal drugs that kill, maim and injure more people in a weekend than cannabis does in a year. But there are two groups who seem particularly vulnerable to the harmful effects of cannabis: heavy users and those who used the drug at an early age.
Like all parents I like to think that my teenage daughters are sensible enough to avoid drugs, but I am realistic enough to know that if they haven't tried cannabis already then there is a good chance that they will. Statistics show that young children are almost as likely to experiment with cannabis as with tobacco. According to a recent survey by the Schools Health Education Unit, one 12-year-old in 16 and one 15-year-old in four now admits to having tried cannabis at least once, up from one in 100 and one in 50 respectively in 1987.
The Government has responded to growing concerns among doctors by performing a U-turn on previous policy and last month upgraded cannabis from Class C to Class B under the Misuse of Drugs Act, a message that it hopes will not go unheeded by young people.
I have never been convinced that the legal status of cannabis makes any real difference to whether a teenager tries it. It has more to do with peer attitudes, and the overriding belief among teenagers today is that cannabis is a bit of harmless fun - the most dangerous thing about a joint being the tobacco that the grass or resin is mixed with. They are mistaken.
Here are a few key facts that all teenagers (and their parents) should be made aware of:
Cannabis damages the lungs: Most people consider cannabis to be much safer than tobacco but, drag for drag, it is actually more harmful. Cannabis smoke is far more acrid than tobacco and causes more damage to the lining of the airways. The British Lung Foundation estimates that smoking an admittedly hefty three to four joints a day causes the same level of damage as smoking 20 cigarettes a day. And, like tobacco, it is packed with carcinogens.
Chest physicians are reporting that a growing number of cannabis users appear to be developing the sort of lung damage normally seen only in middle-aged and elderly smokers - and up to 20 years earlier. And it doesn't seem to make much difference how you smoke it. Research into the relative “safety” of the various smoking devices - joints, bongs, vaporisers and water pipes - found no significant difference in the harmful chemicals inhaled. Because water pipes filter out some of the ingredient (THC) that makes users high, they tend to inhale more of the harmful components to get a decent hit.
Cannabis can cause irreversible changes in the brain: The most alarming discovery in recent years has been that cannabis can trigger serious mental illness such as schizophrenia. As a rough rule of thumb the average person's lifetime risk of developing schizophrenia is about one in 100. This risk increases to about one in 30 in occasional cannabis users and closer to one in 15 in regular users (at least once a day).
The brains of teenagers appear to be particularly susceptible to the drug. A recent study in New Zealand found that children who started to use cannabis before the age of 15 were nearly five times more likely to develop serious mental illness by their late twenties, compared with those who started at 18. Neuroscientists suspect that the greater susceptibility of young teenagers is because the brain continues to develop during the teen years. Drug use is thought to influence this final phase of brain formation, increasing the risk of the type of functional and chemical imbalances associated with conditions such as schizophrenia.
The problem is compounded because most of the cannabis sold in Britain today is much more potent than that of a decade ago. These stronger variants (skunk) contain far more of THC, the active ingredient, which is| thought to induce psychosis, and far less of another ingredient (cannabidiol) found in standard varieties, which is anti-psychotic and protects the brain. But neurochemcal changes don't alter behaviour alone. Tests on mice suggest that they can also permanently disrupt a developing brain's ability to remember things, even after the drug is withdrawn. It is difficult to draw comparisons with human development, but scientists in the field believe that exposure before the age of 15 could cause lasting memory deficit.
Cannabis can be addictive: Contrary to street lore that you cannot become addicted to cannabis, one user in ten develops some form of dependence, with abstinence leading to craving and withdrawal effects. Cannabis abuse now accounts for 10 per cent of attendances at UK drug treatment centres.
Is it a gateway to more dangerous drugs? This is a controversial area. There is little doubt that cannabis users are more likely to try harder drugs such as cocaine and heroin, but this gateway effect is much smaller than we used to think. While most hard drug users start off trying cannabis, most cannabis users don't end up on hard drugs. Only one cannabis user in 25 admits to having tried heroin. That said, the social factors of mixing with peers who are using drugs and having access to supply can only make progression more likely. Age is again a factor - younger cannabis smokers are more likely to move on to hard drugs.
Cannabis and your bones: Recent work indicates that cannabis may accelerate the thinning of the skeleton that occurs as we age. Bone is a living tissue that is constantly being remodelled; cells called osteoblasts lay down bone while osteoclasts dissolve it. Careful balancing of the activities of both groups of cells mean that overall bone mass remains steady - at least until the age of 40 - despite our entire skeleton being replaced every seven years.
Researchers from Aberdeen University have discovered that chemicals found in cannabis may upset this delicate balance in favour of the osteoclasts and bone resorption, leading to osteoporosis - a condition now thought to affect one woman in three, and one man in ten, over the age of 50.
Cannabis and sex: Little is known about the impact of cannabis on sexual function but there is growing anecdotal evidence that it may be linked to shrinking of the testicles and low sex drive in men. Research published this week suggests that it may increase the odds of developing testicular cancer. More research is needed but should any of these links be proved they could become the most powerful deterrent of all for boys and men.
Nothing in life is totally risk-free and all these potential hazards need to be put in context - the vast majority of people who try cannabis will come through the experience unscathed. But for some, particularly those who use it regularly, it will leave a permanent scar that could cost them their friends, family, career and possibly even their lives. At the moment we have no reliable way of identifying those most at risk but we do know that the earlier you start the more dangerous the drug is likely to be.
February 14, 2009
Dr Mark Porter