Why should they waste it on food or clothing or rent or gas or anything else? For the absolutely no difference it makes to you, I don't see why you care in the first place, but more importantly, you're falling into the progressive trap of assuming you know what's best for someone else's life. If someone wants to prioritize some drug over other basic necessities (or cable TV, for that matter), who are you to say they can't, and how do you even know that's the "wrong" decision? What's next - scrutinizing their grocery lists to make sure they're not wasting any taxpayer money on junk food or convenience items (like pre-made salads or meals ready to cook, etc.)?
If you are forcibly taking funds from one group and giving it to another at the very least you should attach some strings.