Hello dear, Most of the weight gain supplements claim to be free from any side effects if taken in the optimum dose. But, they may be harmful if taken for a prolonged time, such as: 1. They contain small amounts of steroids, and can lead to a number of bone-related problems. 2. High amount of protein can affect kidney & liver function. 3. High sugar levels can result in diabetes with long term use. 4. Hormonal imbalances, reduced sexual desire, depression, etc. So, before choosing any such health supplement, it is advisable to consult your family physician once. Moreover, you should not compromise on routine healthy food such as: 1. Consume more of natural diet like fresh fruits, green vegetables, etc. 2. Avoid oily and junk food. 3. Stay away from smoking & alcohol. Wishing you a healthy life. Take care.