It usually starts in the shower. More strands than normal in your hands, then in the drain, then on the pillow. Everyone tells you it's just the weight loss and it'll stop. Sometimes that's true. Sometimes it isn't, and the waiting costs you months.
Before anything else: this is worth taking seriously. Hair loss gets dismissed as vanity, including by the women experiencing it, and that dismissal is why it goes uninvestigated. It's a visible signal that something in your body has changed, and it deserves the same attention as any other symptom.
Cause one: telogen effluvium
The most common cause is telogen effluvium — a temporary shedding triggered by physical stress. Rapid weight loss qualifies. So do surgery, illness, and childbirth. Your hair follicles shift a larger-than-usual share of hairs from the growing phase into the resting phase all at once, and two to three months later that batch sheds together.
Two features make it recognizable. It's diffuse — thinning across your whole head rather than in patches or at the hairline. And it's delayed — it begins two to four months after the weight loss accelerated, not at the same time.
It resolves on its own, typically within about six months, and the hair regrows. Nothing needs to be done except making sure you're not simultaneously running a deficiency, which would extend it.
Cause two: a nutritional gap
The second cause is a genuine shortfall of something your follicles need. Hair is metabolically expensive and non-essential, so it is among the first things your body stops investing in when supply is short. Three nutrients account for most GLP-1-related hair loss.
Iron is the most common of the three in women, especially those still menstruating. Zinc runs a close second, because the body holds almost no reserve and the best sources are the foods hardest to eat on a GLP-1. Both are covered in depth in Part 2 of the Deficiency Series.
Shedding that starts on schedule and stops on schedule is telogen effluvium. Shedding that keeps going past month six is telling you something else.
How to tell which one you have
The practical shortcut: if it's month five or six and shedding is slowing, it was almost certainly telogen effluvium and you can stop worrying. If it's month six and it's the same or worse — or if it's paired with fatigue, cold hands and feet, or things tasting metallic — get ferritin and serum zinc tested.
What actually helps
- Hit your protein target consistently. This is the one intervention that helps regardless of which cause you're dealing with. Hair is made of protein.
- Get ferritin and zinc tested before supplementing iron. Excess iron causes real harm. Zinc at 15–25mg is low-risk; iron is not.
- Slow the rate of loss if you can. Faster weight loss produces more shedding. If you're dropping more than about 1% of bodyweight a week, that's worth raising with your prescriber.
- Be patient with regrowth. Even once the cause is fixed, visible regrowth takes three to six months. New growth appears as short baby hairs at the hairline first.
What doesn't help: expensive hair supplements with dozens of ingredients at token doses, and biotin in particular. Biotin deficiency is rare, supplementing it when you're not deficient does nothing for hair, and it interferes with several common lab tests — including thyroid and cardiac panels. Stop biotin for several days before bloodwork.
Members get the micronutrient gap tracker — which labs to request at each stage, what the results mean, and a monthly live Q&A with our RDN to work through them.
See what's included →Continue to Part 3: Constipation on a GLP-1 — what actually works →