One Out, One In #2: biotin mega-dose → ferritin and TSH

One you drop. One you take instead.

3. Hair gummies are 5–10 milligrams of biotin. The body asked for about 30 micrograms.

2. Milligram biotin can lie to the lab — including a falsely low heart-attack test the FDA linked to a death.

1. If the hair is shedding: ferritin and TSH first. The IN is a test, not another biotin.

Biotin is B7. Adults need about 30 µg a day (Australia: 30 µg men, 25 µg women). There is no upper level because classic overdose is rare. Severe deficiency on a mixed diet has never been reported. One cooked egg is about 10 µg. A piece of beef liver is about 30 µg. Most people already clear the target from food.

The Chemist Warehouse hair lane is not 30 µg.

US hair bottles often go to 10 mg. We did not land a live Australian 10,000 µg SKU this week. The pattern is the same: milligrams sold on a deficiency that almost nobody in the aisle has.

Does biotin grow hair if you are not deficient? The evidence in healthy adults is thin. NIH ODS: hair/skin/nails claims rest on a few case reports and small studies, mostly nails without a placebo, hair only in children with rare shaft disorders. A 2026 systematic review: current evidence does not support routine biotin for alopecia without a documented deficiency. That is not the same as “biotin never helps hair.” It helps if you are actually short. Almost nobody in the gummy queue is.

The real trick is the lab. Many hormone and heart tests use biotin–streptavidin chemistry. Milligram biotin can push them the wrong way: sandwich assays often falsely low, competitive assays often falsely high. TSH can look like Graves on some machines. Troponin can look reassuring when it is not. The FDA reported a patient who died after a falsely low troponin. A single 10 mg dose has interfered with thyroid tests within 24 hours (Biscolla 2017, on the NIH sheet). In six healthy adults, 10 mg a day for a week hit 9 of 23 biotinylated assays (Li 2017). Ferritin was not one of them in that study — do not use that paper to say biotin falsifies iron studies.

Melbourne Pathology put this in the Medical Journal of Australia in 2016: write high-dose biotin on the request form. Some Australian labels say withhold for three days before bloods. That is sponsor / lab advice, not a newsletter order, and it is the wrong move if the biotin is prescribed. The FDA says there is not enough data for a universal hours-before rule.

Park the hair gummy if you bought it for shedding, nails, or “energy.” Keep it only if a clinician put you on high-dose biotin for a real diagnosis.

If the hair is coming out, the grown-up first move is bloods, not a better biotin.

Ask the GP for ferritin and TSH (they will add what else belongs). The American Academy of Dermatology’s public advice is blunt: only take biotin, iron or zinc when a blood test shows a deficiency. Extra iron can poison. We will not print a ferritin “target.” There is no consensus number for hair, and this letter does not diagnose androgenetic alopecia, telogen effluvium, or anything else.

Do not swap the gummy for another gummy. Do not swap it for a hair/skin/nails multi. Those often add zinc, sometimes iron, sometimes B6. The IN is still the test.

If the bloods later show a real shortage — biotin, iron, thyroid — that is GP / dermatologist territory. Not a newsletter SKU.

If it is a hair gummy you bought yourself:

“I’ve been taking high-dose biotin for hair — about 5,000 micrograms a day. Could we check ferritin and TSH, and should this biotin be parked before those blood tests so it doesn’t throw the results? I’ll follow whatever you and the lab advise; I’m not on it as a prescribed medicine.”

If the biotin might be prescribed (metabolic, MS protocol, or you are not sure):

“I take biotin at a high dose. Before any blood tests, including thyroid, troponin or vitamin D, can we tell the lab so they use a method that isn’t fooled by biotin? I don’t want to stop a prescribed product on my own.”