This past week I've had multiple patients, from age 17 to 35, tell me they've stopped the birth control pill--or don't want to start it--because they're afraid of gaining weight. Of all of the side effects attributed to the pill, weight gain causes the most universal fear. I'm glad to be able to tell my patients that the pill will NOT make them gain weight. When they look back at me doubtfully, I tell them three things:

• A fantastic scientific review looked at the best studies that have been published, and didn't find any major effect of the birth control pill on weight. As part of my training, I did a review of almost 200 studies of "observational" trials, and I found the same thing--most women did not gain weight beyond what's expected, about a pound or two a year.

• In many studies where one group of women used birth control pills, and another group of women used placebos, women in BOTH groups had similar effects on weight. Some women gained weight, and some women lost, but most women stayed the same, whether or not they were taking hormones.

• The harsh reality is that over time, most of us gain weight. Our lifestyles change--we eat and exercise differently--and our metabolism changes, too. Some of these changes may happen while we're using the pill. I always felt that the pill was the reason I gained ten pounds when I was in a new relationship and started the Pill again. It took me a while to realize that when I was dating someone seriously, I not only worked out less, but ate out in restaurants more--a bad combination for my weight!

There are many reasons, of course, why we gain weight. If you gain a lot of weight very rapidly, and don't think your diet or your activity level are the cause, talk to your doctor. And I don't have a ready answer for why some of my patients gain a lot of weight on one birth control pill and are fine on another. But in general, the birth control pill is not to blame for weight gain. Have any of you experienced major changes in your weight while on the pill?