What is the ruling on taking medication to gain weight?

A Muslim is required to prepare their body to perform religious and worldly duties. This necessitates achieving physical health and avoiding everything that causes illness or weakens the body. If weight gain occurs through the use of drugs and medicines, there is no harm in that, as long as it does not lead to excessive bulk that hinders the performance of duties or causes illnesses. However, if weight gain occurs through cosmetic procedures in which the body is injected with substances to increase its size, then this is impermissible because it constitutes altering Allah's creation, which we have been forbidden from doing. Furthermore, it may lead to harming the body, and the Prophet, peace and blessings be upon him, said: "There should be neither harming nor reciprocating harm."