Hi, I had gone through your question and understand your concerns. To gain weight, you need to eat more calories than your body uses each day. You need to do this regularly. It s not enough just to have occasional extra snacks Gradual weight gain is always advisable. An increase in 500 kcal per day can result in increasing the body weight by 0.5 kgs per week. Eat plenty of healthy fats. Eat your egg yolks, meat with animal fat, coconut oil, and other healthy fats. Increase caloric intake - of the healthy kind ofcourse. So those bananas count well here. Chew the food properly to improve digestion. Keep a track of your weight gain as this is essential; it is healthy to increase approximately 5 to 6 kgs weight per month. The right combination of healthy food, exercise, right breathing, rest and sleep go a long way in a happier and healthier you. There are medications like Ciplactine and Dexona. Now coming to adverse effects of Ciplactine and dexona. They are nausea, dizziness, restlessness, headache, weakness, stomach upset - to name a few. I would suggest to try the natural way . If it fails , try the medications then. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Wishing you good health.