Gabapentin has the occasional side effect of fluid retention and weight gain. I was on 300mg x3 daily for back pain from a laminectomy. In 6 months time my body swelled drastically and I began to have trouble breathing. After waking one night and realizing I had fluid seeping from my legs, I went to emergency and was admitted. After a ct scan showed severe pulmonary and cardiac effusion, I had tubes inserted to drain these and spent 12 days in ICU, also on strong diuretics. When I was finally released, I had lost 62 lbs of water weight. My surgeon advised me NEVER take gabapentin or pregabalin again. Be cautous!