Human Drug Clinic Vs. Prostitution

I would like to know the difference between selling your body for sex, and selling your body for drugs. Thus, the difference between Human Drug Clinics and Prostitution. The typical argument most people bring up is that Drug Trials are "for the better of the state and human kind". Although, are they not forgetting that they have the similar life-threatening risks? It's still abusing one's body? Somehow, drug clinics are justified, because (if proven beneficial) they can be used for the state? So although the purpose differs, the process is still the same.