I am referring to the gray market: you buy the peptide in powdered form, reconstitute it using bacteriostatic water, store it in the fridge, and inject once a week. The protocols are well known.

Some people titrate (adjust the dose up every two weeks), others stay at the same dose as the initial one (1-2 mg per week), and some fit people use half of the initial dose (0.5 mg per week). Retatrutide/GLP-3, which has yet to be approved for human use (FDA is expected to give the thumbs up by the end of the year), is used, I'd venture to guess, by millions of people at this point.