The paid channels are closed, and most clinics find out by getting suspended
Google restricts prescription drug advertising to certified advertisers and does not accept ads for unapproved pharmaceuticals. Compounded peptides sit on the wrong side of that line often enough that a campaign built around compound names is a suspension waiting to happen, and a suspended account is harder to get back than it was to lose.
Clinics respond by advertising vaguely — wellness, optimization, longevity — which passes review and converts nobody, because the person searching for a specific compound does not recognise themselves in it. The budget gets spent proving that the channel does not work, when the real finding is that the message had to be stripped of everything useful to survive review.