All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
There is no harm in taking steroids or medicines that increase weight on the condition that taking them does not cause a greater harm than the benefit of increasing weight, and on the condition that its ingredients do not contain any forbidden item like pork or any extracts from animals that are not slaughtered according to Islaamic rites.
Allaah knows best.