Five hundred studies, mostly mice

The compounds in the gym-recovery conversation have always carried a certain confidence. BPC-157 for the sore tendon, TB-500 for the next one, a growth-hormone peptide to tie the week together. The pitch moves quickly, and it tends to skip the part where somebody checks. A review out of UCLA this fall did the slow thing instead. It counted.

The count

A team led by sports-medicine physician Thomas Kremen, with medical student Kushagra Tewari, pulled together 565 studies on six compounds commonly sold for recovery and performance: BPC-157, TB-500, CJC-1295, ipamorelin, GHK-Cu, and MK-677. Five of those are peptides. MK-677 is a small molecule that travels in the same crowd, which is itself a small lesson in how loosely the word "peptide" gets used on a sales page.

The review followed PRISMA, the standard recipe for this kind of survey. In practice that mostly means the search terms and the rules for what counts are written down before the counting begins, so the result is harder to steer toward a conclusion someone already wanted. It was published in the American Journal of Sports Medicine in early September.

What the pile adds up to

More than two-thirds of the 565 studies were done only in animals. That is the number to sit with. The rodent work showed real but variable effects on tendon, muscle, bone, and ligament, and rodents are not small people. A healing signal in a mouse is a reason to run the next study, not a reason to believe the last one.

The human studies that did exist were small, and they showed modest or unclear benefit for the outcomes people actually reach for these compounds hoping to change: faster healing, a quicker return to sport, better performance. After years of interest and hundreds of papers, the thing being sold has not been shown, in people, to do the thing.

The authors put it more plainly than reviews usually do. "The evidence that these peptides are effective is just not there," Kremen said. The marketing, in his phrasing, is well ahead of the science.

The part that should slow you down

An absence of proven benefit is one finding. The review flags a second one that matters more. These products sit outside FDA oversight, so what is in the vial is its own open question. Testing has turned up contaminants including arsenic and lead, and much of the supply arrives labeled "not for human use" before it is repackaged and sold on. One MK-677 trial was stopped early after a rise in congestive heart failure among participants. Kremen also described a patient whose cardiac output fell to a dangerous low while using peptides.

None of that proves these compounds are broadly harmful. It says the honest risk column is not blank, and that "natural recovery peptide" is doing a lot of quiet work to make it feel blank.

How to hold it

A null result is still a result, and this is a useful one. The review does not show that these molecules do nothing. It shows that the case for them, taken as a whole and read strictly, rests mostly on animals, and that the human floor under it is thinner than the volume of conversation suggests. That is a specific, checkable claim, and it is more than most of the marketing can offer.

This blog has written about several of these one compound at a time. What the UCLA survey adds is the view from above: the same story, told at the level of the whole shelf rather than a single bottle. The mechanisms are often real. The mouse data is often promising. The distance between that and a person getting a reliable benefit is exactly the distance the science has not yet crossed, and pretending otherwise is how the marketing got out ahead in the first place.

The patient move is the old one. Wait for the human evidence to show up, or admit clearly that it hasn't.

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This post is educational and general in nature. It is not medical advice. For guidance about your own health, talk to a qualified clinician.