Food is best medicine instead of taking medicine which are not safe and may have side effects you should consult dietitian. Weight gain is a slow process it take time. And it need well planned balanced diet
along with physical activity and proper rest. You need well plan diet suited to your needs. Mean while here are few tips for you- Start eating small frequent energy dense meals instead of 3 large meal. Small meals are easy to digest and keep digestive system running. You can eat small portion of healthy food in difference of 2-3 hours have shakes of fruits with added nuts drink atleast 8-10 glasses of water. Eat all seasonal fruits and vegetables. Manage stress Quit smoking
or drinking if any do some moderate intensity exercises for 30 minutes daily. Have positive body image appreciate your self Take sound sleep of 7-9 hour keep your self motivated as it not going to happen overnight. Consult me online
for better results.