There was with yaoi it was like either a one shot or an extra chapter from a different manga all I remember was there was this guy and he needed money and he needed a place to live and a guy he knows is like researcher and he needed someone to take an experimental drug I think it was a aphrodisiac and anyway they started living together and he was feeding hip the medicines and having sex or sexual like things. One day the guy was at work and coworkers were saying how his skin has been looking really nice. He realized that yeah he has been feeling healthy and stuff. He runs into a friend and he saw the researcher guy saw him at a store and just dumped a whole bunch vitamins in a basket to buy. It turns out he has been feeding him vitamins and not an experimental drug. He confronts him angry that he was being duped. Around the end the researcher/doctor person confesses that he liked him and used the drugs as an excuse to sleep with him.

That's all I can remember if anyone knows please tell me the title.

Quote from xclusivek0rean

One day the guy was at work and coworkers were saying how his skin has been looking really nice. He realized that yeah he has been feeling healthy and stuff. He runs into a friend and he saw the researcher guy saw him at a store and just dumped a whole bunch vitamins in a basket to buy.

The side/extra story included in Volumes 1 & 2 of Usagi Otoko Tora Otoko--specifically Volume 2, Chapter 3--has a scene very similar to this. However, it's probably not the one you're seeking as a number of other details differ from the rest of your description. (For example, I don't think the main characters end up living or sleeping together...yet!)