Can codeine cause weight gain?

Very rare.: Not much more to say. All medications have side effects but weight gain is listed as very rare for codeine. If you experience weight gain with no other changes is medications or lifestyle then this may be a side effect and should be discussed with you physician.

Yes and No: I do not see how Codeine itself can cause weight gain, however the relief of pain and the "feel good" effects of a lot of different drugs (not just codeine) can increase you appetite, you eat more, and wallah! you get fat.