Benefit

Shaykh Ibn ʿUthaymīn رحمه الله said:

“Curing oneself with impermissible substances* is not able to be called a necessity due to two reasons:

The first: a person may become better without any cure, so, with this in mind, it cannot be a necessity.

The second: the ill person could take it and not become better, and in this case, the necessity has not been removed by it. For this reason, the statement of the laymen that “it is permissible to cure oneself with something impermissible due to a necessity” has no validity to it. The ʿulamāʾ رحمهم الله have ruled that it is impermissible to cure oneself using impermissible substances.“

Sharḥ al-Arbaʿīn al-Nawawīyyah (167)

E.g. cannabis, marijuana, alcohol, etc..