There is good human evidence that GHK-cu has beneficial effects on skin topically, but realistically that is about it for human clinical trial evidence.
No ethics committee would approve a trial of systemically administered KLOW or GLOW , based on their complex wide ranging and poorly understood effects of the individual components let alone them all combined. And the lack of even any animal testing.
The fact that so many people say it works does look convincing. I did have a discussion with chatgpt about this while ago.
An individual who uses these blends of peptides and finds they worked for them has experienced it working, but outside the context of a clinical trial where biases are accounted for and controls are present, it does not prove it will work for others. At best it is suggestive anecdotal evidence.
There are reasons why it could do nothing and yet look like it works.
Generally people start treating something when it is at it's worst, so that when the severity of the problem regresses back towards the mean over time, it will look effective.
Chronic soft tissue inflammatory / age related connective tissue degradation type problems it is often claimed to fix do have highly variable degrees of symptoms over time.
And of course the placebo effect, the degree to which the effects of those peptides have been repeated online, is very effective in convincing people it must be true if so many people say it, which is going to enhance the placebo effect, and as long as it is not causing harm, then this is actually then a useful treatment.
My logic is that if it is truly effective at increasing growth of connective tissue , then it carries risks of causing that growth in places you do not want it to happen, such as the heart or liver, which could cause organ function damage or failure long term. So if it does work as advertised it could be unsafe, and if not then at best it is a placebo.