The first dose of a copycat weight-loss drug Lindsay Posey took from a new pharmacy worked well. The second didn’t quite suppress her appetite. It was the third dose that she thinks caused her trouble.

Acne erupted on her cheeks, nose, chin and forehead. “My skin just went absolutely crazy,” said the 38-year-old who works in online customer service. Acne isn’t listed as a side effect of the FDA-approved formulation.

Posey had resorted to buying the knock-off medicine through a telehealth company because she didn’t think her insurance would cover the brand-name version. She trusted the situation because the drugs were made at a licensed facility in the US. “It just seemed safe,” she said.

Her doctor suggested it might have been a problem with the medicine itself. “That’s not really something you want to hear,” Posey said. The drugs were produced without going through the rigorous approval process required for brand-name or generic medications.

They are made by so-called compounding pharmacies, an obscure corner of America’s pharmaceutical market that relies on a legal loophole to produce copies of treatments in short supply. Doctors worry this shadow industry may be putting patients at risk. Normally focused on producing bespoke therapies, these pharmacies started making copies of weight-loss drugs en masse after demand outstripped the supply of Eli Lilly & Co.

’s and Novo Nordisk A/S’s medications. Health insurers aren’t racing to cover the roughly .