Hi ME!   Weight gain is a poteintial side effect of Nortriptyline, but for someone to tell you 100% for sure if you personally are going to gain weight......no one can do that.   Each medication effects a person differently. That being said, side effects that you may get on a medication, another person on the same medication may not get. You have to remember, your doctor is prescribing you a drug because what it will (should) do for you will hopefully outweigh the side effects. Having no migraines, or a drastic cut in migraine frequency is worth an extra 5lbs don't you think?   You would have to try the drug and see how it effects you. If you see a huge weight gain - then you can talk to your doctor about changing your medication. Remember, Nortirptyline is not your only option. There are over 100 medications being used for migraine prevention.   I am currenlty taking Amitriptyline, which has the same side effect of weight gain, so every time I go to the doctor, we talk about it and I hop on the scale.   Hope this clears this up some.   good luck!