I don't think that using drugs is morally evil, it has to do with the reasons why they are used, the moment in which it is done, and the potential effects it can have on a person, what determines if it is a responsible use, and therefore, morally good, but using drugs alone I don't think is morally evil.

I personally wouldn't do it, I don't even use pharmaceutical drugs, I don't like it, but not because it's morally wrong.

Now, maybe the act of buying drugs can compromise the morality of a person, because you are giving the money to people who may be capable of killing, who may be corrupt, who may be corrupting society, who may even be linked to politics and state power, and that they are actually doing evil, and that you would be supporting by giving them your money. I'm not saying it's always like this, but it's a possibility.

In the end, it all depends.