Hair shedding shows up for a lot of GLP-1 users somewhere between month three and month six. It is real, it is usually temporary, and it is almost always downstream of rapid weight loss rather than the medication itself.
The mechanism
The clinical name is telogen effluvium. Any sharp physiological stress (surgery, illness, childbirth, a big calorie deficit) can push a larger-than-normal share of hair follicles into the resting phase. Those hairs then shed a few months later, on schedule. It looks alarming. In most cases the follicles are not damaged; they cycle back on their own.
Nutrient status in the research
Protein
Hair is basically protein. Under-eating protein is a documented driver of shedding.
Iron and vitamin D status
What does not help
Biotin megadoses are the classic sell here. In people without a true biotin deficiency (which is rare in the US), the research does not support supra-physiologic biotin for hair growth. High-dose biotin also interferes with common lab tests, including thyroid and troponin.