Hi, Unfortunately, there are possible side effects of any medication. Biotin should not cause any significant weight gain to occur. Medications can cause weight gain can occur in different ways- they can increase appetite, they can decrease energy and therefore activity level, they can decrease fullness or alter metabolism. Most of these can be combat with monitoring diet and purposely increasing activity. The use of thyroid hormone replacement would help to decrease the weight cause by low levels of thyroid hormone. This weight loss would reduce your acne. Biotin can worsen acne in some persons. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Michelle Gibson James, General & Family Physician