Hye,
Thanks for the query.
Side effects of supplementation only happens if you take it without it being needed by the body. Unless you create a demand supplemention cannot work.
The moment you think of weight gain, whatever is your workout or diet intake, does not justify taking a supplement.
You cannot gain weight by just adding a supplement to your diet.
Weight gain needs additional calories through a balance of carbohydrates, proteins, healthy fats and exercise.
Supplementation totally depends on your present food intake & activity levels.
So, for weight gain you need a balanced, calorie dense diet and a good exercise routine.
Even if you do gain weight it will reduce once you discontinue the supplement.
So, before enough decide to start the supplement first work on a healthy diet and exercise routine.
So, for supplement to work first you need to concentrate on improving your diet.