How dangerous is anti-smoking drug?

The anti-smoking drug varenicline (brand name Champix in NZ, Chantrix in US) is in the news because of risks of heart disease.  Recent summaries of research suggest that varenicline increases the risk of serious cardiovascular disease by about 70%. “Serious”, here, is a grab-bag of diagnoses, but they are all things that at best will put you in hospital and at worst are fatal.  Smokers are already at higher risk of cardiovascular disease, so this sounds bad.  On the other hand, varenicline is supposed to help stop smoking, and that will decrease the risk of cardiovascular disease.

How do the risks balance out? Well, that depends on a lot of details, which is why MEDSAFE doesn’t want to commit itself until they’ve had a chance to look at all the evidence.  Still, smoking increases the risk of serious cardiovascular disease by a factor of three to six, and nearly all this increased risk goes away rapidly if you stop smoking.  Varenicline increases the chance of successfully stopping smoking by about 10 percentage points, so we can run some examples with plausible numbers.

Suppose you have 1000 smokers with pretty high risk, who have a 4% chance of a heart attack or death in any given year.  In the six months trying to quit you would expect 100×0.04/2=20 heart attacks without varencline, or 35 with the drug, an excess of 15.  Now, for 900 of these people the drug didn’t have any impact on quitting — they either would have succeeded anyway or would have failed anyway.  That leaves 100 people who were helped to quit, which will save about 3 heart attacks a year for the rest of their lives.   The break-even point is about five years later, and that’s ignoring the other health benefits of quitting.   The basic calculation works the same way for lower-risk smokers — the benefit is smaller, but so is the risk.  Varenicline looks pretty good now.

There are two complications. The first is that there is a lot of uncertainty in both the benefits and risks.  If varenicline actually increases risk 150% and only gets 5% more people to quit, the break-even time is more like 20 years, and the benefits look more dubious. That’s especially true when you consider the other side-effects.  It’s been known for years that varenicline is no fun at all to take, and in particular there are accumulating reports of serious depression.

As usual, PHARMAC seems to have a sensible policy on the drug — the government will subsidise it, but only if you’ve unsuccessfully tried simpler and safer approaches to quitting, like patches or nicotine gum.