I'm not taking Activella but I am a pharmacist. I looked at the prescribing information (
http://www.novo-pi.com/activella.pdf), which summarizes the side effects reported during clinical trials performed to obtain approval from FDA of the drug. Weight loss is a possible side effect, although weight gain is considered more common. Fluid retention is a possible side effect. None of the women taking the drug to treat menopausal hot flashes in studies lasting 3 months experienced weight gain. Nine percent of women taking the drug for 2 years to prevent osteoporosis gained weight, but 6% of women in these studies taking placebo (a sugar pill) gained weight. Please keep in mind that many women participating in the studies were not exercising or watching what they ate the way you are. I hope this places into perspective for you the risk of weight gain. It strikes me as unlikely that you'll gain weight while taking Activella if you continue to work out and eat sensibly as you always have, but ask your ob/gyn if you are concerned. You didn't say for how long you plan to take the drug.