Hi!   It depends. It may be too much weight gain too fast, but you need to talk to your doctor about it. Rapid weight gain can be a sign of several medical conditions, so you should talk to your doctor to either diagnose or rule out any of those conditions.   Are you taking Periactin on a  doctor's recommendation? Are you taking Periactin for allergies? Or are you taking Periactin specifically to gain weight?   I think it is unwise to take a medication for anything other than its intended use without the direction of your physician.   Bottom line -- you should talk to your doctor about this. Keep in mind, it is much harder to lose weight than to gain weight, so you want to make sure you are healthy regardless of the actual number on the scale.