In PoA, the Wolfsbane Potion is made by Snape for Lupin during Lupin's stay at Hogwarts. But what does Lupin do without drinking the potion? This applies to after he leaves Hogwarts as a student (when he was supposed to transform in the Shrieking Shack) up to PoA and during OotP-HBP. I suppose it depends on where he's living, but he can't possibly just allow himself to turn into a monster once a month and run wild. Especially in OotP, when he's living in 12 Grimmauld Place, which is in the middle of London.

Maybe he goes somewhere every month for the full moon where there aren't many people, such as a forest, etc. What do you think?

I'm sure he has someone else make it for him. Or maybe Snape makes it for him all the time. We know very little about what the teachers do outside of school or during holidays. Prehaps Snape makes barrels of the potion so Lupin always has a supply at hand.

I don't think Lupin is using the potion very much though. He is currently assigned to undercover work with Fenrir Greyback and his gang of werewolves. This would also explain his looking ragged in HBP.

Interesting question. I know he has been living with the werewolves because that is where he learns of Greyback's desire to bite all the children that he can. I would say that other people beside Snape would possibly be good at making the potion, or perhaps DD has convinced Snape to make him a lasting supply. I would say that there is someone who is helping to not attack people, and or he is going somewhere that is deemed safe for him to transform without there being threat to people.

he might just go to someone and get the potion, or he might do want you said and go to a forest.that would be my guess.

Maybe he only transforms if he actually sees the moon so if he stays inside he wouldnt transform? I mean in PoA he didnt transform until they were outside in the moonlight