hai, Your doctor clarification regarding copper T and weight gain is scientifically true. copper T will not cause any weight loss. As your BMI says you are under weight. I will advise you to gain weight in healthy way. Increase your calorie intake by ; taking protein nourished foods like Almond,cashew,channa,soyabean,peanut in your daily food intake. add milk and milk products in your daily diet plan. wheat and dal prepared with ghee,jaggery.and tuber vegetables like potato and fruits like dates,fig,banana can be taken,. be hydrated. Avoid stress. This will nourish in a healthy way to gain weight. no need for medication unless there is a abnormality. hope i answered your query thank you