Medical cannabis use carries a risk of dependence and of lung cancer

I like to make my position clear from the outset: I support the legalization of cannabis (marijuana and hashish). I think criminalizing it makes criminals out of otherwise upstanding people who use it recreationally, either harmlessly or harmfully (of more, anon). And criminalizing it is a latter-day prohibition, often putting its sale in the hands of organized (and, frankly, disorganized) crime. The fact that cannabis has been illegal has never stopped anyone in Canada from using it and has probably stopped users from admitting their use to their doctor, social worker, parents, etc.

But does it have legitimate medical benefits? Should it be used to help with symptom control in pain, chronic neurodegenerative diseases and so on? Should it be prescribed and monitored, rather than just leaving patients to buy it at Shoppers Drug Mart and experiment with the dosage?

This spring, I attended a panel discussion by cannabis producers as part of the Science Writers and Communicators of Canada conference in Vancouver. Naturally, the producers were in favour of the medical use of cannabis, as this is a potential market for them. It also gives the leaf a patina of credibility and respectability.

I am all in favour of treating cannabis as a potential drug, including research into its safety and effectiveness and licensing for proven uses.

But I heard a few things said that were untrue, skirting serious issues in the medical use of cannabis. Sometimes I wondered whether the speakers had been smoking something.

I want to review a few things that were said.

  • Only 3% of cannabis users become dependent.
  • Cannabis doesn’t cause lung cancer, or does so at lower rates than tobacco.

Let’s look at these claims. The best study I have found on rates of cannabis dependence is a 2012 review of data to date [Degenhardt and Hall (2012). Extent of illicit drug use and dependence, and their contribution to the global burden of disease. The Lancet 379(9810): 55-70].

It found a 9% rate of dependence among users.

A later study by the same authors estimated the rate of cannabis dependence in Canada at 0.6% of the high-income population in 2010 [Degenhardt et al. (2013). The global epidemiology and contribution of cannabis use and dependence to the global burden of disease: results from the GBD 2010 study. PLoS One 8(10): e76635, Table S4]. The rate is undoubtedly higher for the low-income population, as the authors’ 2012 study found.

This is in line with the recent Statistics Canada survey that found that 14% of Canadians over 15 had used cannabis recently (previous three months), with 56% of that 14% saying they used cannabis daily or weekly.

I have seen people become dependent on cannabis, and my observations are in line with the higher estimates.

So, definitely more than 3% of users.

But whether it causes dependence shouldn’t matter anyway, because, evidently, smoking cannabis doesn’t cause lung cancer. Except that it certainly does.

In fact, it increases the overall risk by five times, according to a case–control study carried out in New Zealand and published in 2008 (Eur Respir J. 2008 Feb; 31(2): 280–286. doi: 10.1183/09031936.00065707. For each year of cannabis smoking, the risk increased 8%.

For every study, there is another that contradicts it. Some other studies have not found this association. One of the problems is that a lot of people who smoke cannabis also smoke tobacco, or smoke both together. The New Zealand study used statistical analysis to separate the effects of cannabis smoking from tobacco smoking, but some other studies have not found a separate effect.

An analysis that combined data from several studies had mixed conclusions [Int J Cancer. 2015 Feb 15; 136(4): 894–903]. On one hand, the authors found that having ever smoked cannabis did not alter the overall risk of lung cancer. On the other hand, risk was clearly higher when they looked at a particular kind of lung cancer – adenocarcinoma – especially if the patient smoked a joint or more per day, and especially if they had smoked for more than 10 years. The difference also showed up in people who had smoked cannabis for 20 years or more, for all types of lung cancer.

OK, the risk of lung cancer associated with cannabis smoking appears to be lower than the 23-fold higher risk linked to tobacco smoking (US estimate in men only). But yes, you could get lung cancer.

There is a growing body of evidence on medical use of cannabis, and more trials are needed. I’ll try to get to this in future blog posts.

But arguments for medical use are not helped by unsupported statements and claims. Risks of dependence and lung disease need to be addressed in medical use. Downplaying them or wishing them away doesn’t help anybody.

BC provincial government site publishes unsupported lifestyle advice on hot flashes

At the risk of being a one-note Johnny, I am very concerned when lifestyle advice to menopausal women from normally credible, reputable sources is unsupported by evidence, at best, or is basically old-wives’ tales, at worst. If other health information were based on such equivocal and weak evidence, it would not be considered acceptable.

The Globe and Mail recently published a lifestyle article on hormone therapy for hot flashes, which I read with interest. It mentioned that HealthLink BC, a patient health information site run by the government of British Columbia, was recommending lifestyle advice that my own literature review indicates is unsupported. By contrast, its advice on medical therapy is generally referenced and based on evidence.

This is what HealthLinkBC says:

  • Avoid using tobacco or drinking a lot of alcohol. They tend to make hot flashes worse.

The evidence on both of these is equivocal (see my previous post). There is some limited evidence from well-designed observational studies that never smoking and quitting smoking are associated with fewer hot flashes. The evidence on alcohol is mixed, with some studies showing alcohol decreases hot flashes.

  • Manage stress. Stress can make hot flashes worse.

Well, there is evidence showing that being happy and contented actually increases hot flashes and stress decreases them. There is little good evidence about effects of stress.

  • Exercise regularly, and eat a healthy diet.

As I indicated in my earlier post, the evidence on exercise is mixed and shows only modest changes. There is evidence that obesity (but not healthy weight) is associated with hot flashes, so losing weight is advisable as a way to decrease hot flashes only if you are obese.

  • Try rhythmic breathing exercises. This is called paced respiration. It can help you meditate and relax, and it may reduce your hot flashes.

OK, the first randomized controlled trial on this recently reported. There was a modest (less than 20%) decrease in hot flashes in the group that used this paced respiration method in which you slow your resting breathing rate (kind of conflicts with the exercise advice). But (get this) the control group, which listened to music instead, had a 44% decrease in hot flashes. Keeping in mind that placebo effect is huge in hot flashes, we should all be listening to music rather than breathing slowly.

  • Drink cold liquids rather than hot ones.

Hot liquids (and anything hot) can bring on a hot flash, but there is no evidence that they increase the overall frequency or severity of hot flashes.

  • Eat smaller, more frequent meals. Digesting a lot of food can make you feel hotter.

No evidence. Also, while the immediate trigger of a hot flash may be warm ambient temperature and other heat sources, the problem is not that women affected are overly hot. Menopausal women in Canada have hot flashes in minus 20 degree Celsius weather. Hot flashes do not feel like being hot from ambient temperature or exercise, and body temperature before a hot flash is normal and then actually rises measurably during the hot flash.

  • Stay cool
  • Keep your area cool. Use a fan.
  • Dress in layers. Then you can remove clothes as needed.
  • Wear natural fabrics, such as cotton and silk.
  • Sleep with fewer blankets.

Staying cool does help prevent the immediate onset of hot flashes and helps women recover from them quickly when they occur. However, from personal experience, I’m not sure it reduces the overall frequency.

No evidence.

From HealthLinkBC’s medical therapy section:

  • Black cohosh may reduce or prevent hot flashes, depression, and anxiety.

There is a reference for the paragraph containing this statement to a Health Canada page on traditional herbal use of black cohosh, which includes menopausal symptoms. There is no reference to the medical literature, which has plenty on black cohosh. There have been some small randomized controlled trials (around 300 patients) showing benefit of black cohosh in hot flashes and published in a respected, peer-reviewed journal (Obstetrics and Gynecology). However, a Cochrane systematic review pooling data from 16 randomized controlled trials involving more than 2000 women with menopausal symptoms found “insufficient evidence to support the use of black cohosh for menopausal symptoms.” However, since some studies found some benefit, the review called for more research on this traditional herbal remedy.

I find a lot of information for patients tries to get around the fact that the evidence is poor by using words like “may” or “might.” As in, “black cohost may reduce or prevent hot flashes.” Or it may not. I suspect many patient-readers looking for something to try are not going to pick up on the subtle distinction of a remedy that may or will provide some benefit. And this is concerning, as many herbal remedies are not risk-free. Black cohosh has been linked with liver-damage events in people who have taken it, although a meta-analysis of black cohosh studies found no evidence of liver problems. Black cohosh may or may not have risky side effects.

But why not just be upfront with readers about the state of the research evidence on various lifestyle advice and herbal remedies? And why tell women something is going to help when it isn’t? I also find that a lot of patient advice is good, general health advice. But it’s like health authorities are trying to trick readers into following advice by selling it as something that’s going to help with a particular problem.

There are lots of good reasons to eat properly, quit smoking and limit alcohol. Like heart disease, cancer and diabetes. Don’t tell women healthy living will help their hot flashes when it won’t.