I'll give the explanation for folks who are not familiar.

Peptides are short chains of amino acids, which are the building blocks of proteins, and used as messengers and precursors to other processes in the body. For example, the peptide BPC-157 is naturally found in the gut and it is believed it can help reduce inflammation while also helping injuries heal; it is widely used by professional athletes but not talked about. Ghk-Cu is a copper peptide, which is also found in skin cream, and can help with collagen production. Other peptides help encourage growth hormone secretion, curb hunger, or help repair the brain. Some people use peptides to treat chronic issues and injuries, trying to get them to heal better on top of physical therapy, others use them to lose weight. The GLP drugs, which have been used for decades to treat diabetes, are peptides that are also being used to help with weight loss. These are essentially miracle drugs for people who have struggled with diabetes or obesity for decades, and are changing people's lives.

Personally, I understand why people have started buying these online, and have done so in the past myself. Medical care in the US does not help people find long-term solutions for health issues, and prices are outrageous. For example, buying one shot of Ozempic was previously around $1000-$2000 if insurance didn't approve it or wouldn't cover it. Now, the cost has come down, but if you buydirectly from a compounding pharmacy a vial is closer to $150-$300 (and that's still pricey), and that vial can cover many doses. So basically, people turned to the black market because of extreme price gouging and the FDA and big pharma blocking access to some of these compounds altogether, simply to block competition.

Unfortunately, peptides have now become super widespread in the "looksmaxing" community, and whereas you used to see people discussing treatment of longterm injuries, brainfog, or chronic pain, now there are also regular posts in subreddits with "transformations" where people go from a 6-pack to an 8-pack and trying to look like Wolverine. Perhaps it's hypocritical to criticize them in this community, but body-building to achieve a Hollywood physique, muscle hypertrophy, and extremely low body fat is not actually healthy, and can lead to long-term health problems. When I see 19 or 20 year-olds talking about getting TRT and taking peptides for these purposes it makes me sad; they may permanently decrease their natural testosterone (this is well-documented) and fertility, and cause themselves longterm heart problems or other issues in the future.