PRESCRIPTION DRUGS

The theory: It’s the meds. Many drugs have the added side effect of endowing people who take them with added pounds.

And this happens more now because, in general, these drugs are much more widely used than they were 30 years ago (when some didn’t even exist).

The research: Weight gain is a known side effect of many drugs, including powerful antipsychotics, over-the-counter antihistamines, antidepressants, diabetes drugs, beta blockers and corticosteroids. Oral contraceptives have often been implicated too, though a 2006 review paper found no evidence of a connection.

Reasons for this burgeoning embonpoint aren’t yet clear, though at least some drugs seem to make patients hungrier, and beta blockers may lower a patient’s metabolic rate.

A 2000 review article found weight gain can be a sign that antidepressants are working if patients who lost weight when they started being depressed gain some back when they stop (though no one thinks that’s the whole story).

Not all drugs of any one type are equally fattening. For instance, metformin is one diabetes drug not associated with weight gain, and some newer beta blockers aren’t either, but older ones are.

Antipsychotics are probably the biggest problems – leading some patients to gain as much as 100 pounds in a year.

Use of these prescription drugs has increased a lot. Some drugs associated with weight gain weren’t even on the market 30 years ago. Others are prescribed much more than they used to be.

One 2003 study showed that U.S. use of oral antidiabetics more than doubled from 1990 to 2001.

Our experts weigh in: The consensus is that, yes, drugs can cause weight gain. But just as with smoking, even if effects are big in subgroups of the population, they don’t necessarily pack much of a punch in the population as a whole.

“This is a contribution to the obesity epidemic, but again, I would not say this is a big contributor,” says James Hill of the University of Colorado.