"It's only a blood pressure tablet"

The tablet is small and the condition is invisible, and it's easy to conclude that whatever it's doing is small too. So this chapter is about what the numbers say and, just as carefully, what they don't.

The review of 44 studies I mentioned in chapter 4 found that people who took their blood pressure medicines well, meaning at least 80 percent of doses, had about a fifth lower rate of cardiovascular disease than those who didn't, and for statins about 15 percent lower. Deaths from any cause were lower too, by more. A broader review of 63 studies across many conditions found that the difference in outcomes between high and low adherence was about 26 percent overall. These are large effects for a small tablet.

Now the caution, because it's the honest one and you'd find it anyway. In 2006 Simpson and colleagues pooled 21 studies of adherence and death, including eight where some participants had been given a placebo, and found that people who took their placebo reliably also died less often than people who didn't. Taking your tablets well, in other words, goes along with being the kind of person who does other things well too, and part of the benefit in the adherence studies is that, not the tablet. Researchers call it the healthy adherer effect and it's real.

What it doesn't do is rescue the drawer. The placebo takers weren't healthier because of the sugar pill. They were healthier because they did the things, and taking the tablet was one of the things. Meanwhile the trials that got these medicines licensed, which compared the medicine to placebo in people taking both properly, are where the benefit of the tablet itself was shown. Both are true. The tablet does something, and the person who takes it reliably tends to be doing other good things, and neither is an argument for taking it on Tuesdays.

So it's only a blood pressure tablet in the sense that it's small, and cheap, and boring. What it's for isn't any of those.