"belviq gave me horrible headaches when i started taking it and if i forgot to take it (when the meds left my system). at first it didn&#039;t do anything for me, then after taking it for 4 months, i gained 20 pounds. i&#039;ve read this medicine works similarly to antidepressants and i&#039;ve had weight gain problems with antidepressants in the past, so i&#039;m thinking that&#039;s why this medication did not work for me."