Welcome Regigirl,

To me it seems like:

Savella was made for depression but used for fibromyalgia pain, like Cymbalta. It is a selective norepinephrine and serotonin reuptake inhibitor. It inhibits norepinephrine uptake with greater potency than serotonin.

Cymbalta is a selective serotonin and norepinephrine reuptake inhibitor too. It's a little bit like this drug, but Savella concentrates on norepinephrine reuptake more than serotonin.

That's my take on this. Ask your Pharmacist. Both are suppose to help with pain, but Cymbalta and Savella are both known to help treat depression.

As for weigth gain, when you are not in pain and feeling better, you probably feel like eating more. I think both of these drugs list decreased appetite as a side effect. We are all unique, so it's possible that one might affect a person in a different way, than the next person.

I hope it helps you. Good luck.