You should definitely ask your doctor first. I wouldn't mess with blood pressure medication on my own.

I take metoprolol tartrate, which is a beta blocker (which I didn't know until just now when I looked it up). It's not for blood pressure, strictly speaking -- I had a weird heart issue a few years back and they put me on metoprolol and warfarin afterward. I successfully campaigned to get off the warfarin a year later, but I'm still on the metoprolol.

I've been taking it for over 3½ years, and during that time I've been able to lose weight. Within a few months of starting it, I began a program during which I lost 70 pounds over about five months. I've lost at various other times in the years since, and earlier this year I lost about 25 pounds as part of a seminar/boot camp program. In both cases (the 70-lb. loss and the 25-lb. loss) I made some pretty radical changes to my overall lifestyle.

The only thing I think I've noticed about metoprolol is that it seems to prevent me from getting my heart rate up toward my supposed maximum and/or sustaining it in optimal range for as long as I'd like. I haven't worn a heart rate monitor during exercise very often, but I did pretty frequently during boot camp, and I wasn't seeing the kind of rates I would have expected -- which I attributed to the metoprolol. Still, I was losing weight pretty reliably.

Talk to your doctor.