Biotin: morning or night?

Either, slot does not matter. Biotin is not stimulating, not sedating, and its effects (when present) build over months. Pick the meal you are most consistent about, and pair with a B-complex if you already take one. The only timing rule that matters is the 72-hour pause before lab tests.

Biotin (Vitamin B7) is a water-soluble B vitamin and cofactor for five carboxylase enzymes involved in fatty acid synthesis, gluconeogenesis, and amino acid metabolism. True biotin deficiency is rare (gut bacteria synthesise some, and the RDA of 30 mcg is easily met by a normal diet), so the popular hair, skin, and nail claims work mainly when an underlying deficiency exists. Time of day is essentially irrelevant for biotin, what matters is daily consistency over months and, critically, pausing supplementation before lab tests. The FDA has issued safety communications about biotin interfering with immunoassays for thyroid hormones, troponin (cardiac biomarker), parathyroid hormone, vitamin D, and several other hormone tests, sometimes producing misleadingly normal or abnormal results. Doses above 5 mg per day can interfere; doses above 10 mg per day reliably interfere.

The windows above are anchored to a conventional day, not to clock time. If you work nights or wake at midday, shift the whole pattern rather than the individual dose: treat your own waking hour as "morning" and your own wind-down hour as "night". For Biotin the thing that matters is the relationship to your sleep and to your meals, not the number on the clock. Shift workers rotating between days and nights get the most consistent results by anchoring the dose to a fixed event, the first meal of a shift, rather than to a fixed time.

Take it later the same day if there is still a sensible slot left, with water at any point. If the day is gone, skip it and resume tomorrow. Do not double the next dose to compensate: for anything stored in the body a single miss is inconsequential, and for anything cleared quickly a double dose gives no benefit while raising the chance of side effects. Adherence over weeks matters far more than any single perfectly timed dose, which is why the best window for Biotin is usually the one you will actually keep.

• Any consistent slot

  Pick a meal you'll remember; pair with a B-complex if you take one.

• Does biotin really grow hair?+

  In people with measurable biotin deficiency, yes, supplementation reverses the deficiency-related hair changes. In healthy adults without deficiency, evidence for accelerated hair growth at 5,000 to 10,000 mcg per day is weak. If you have thinning hair, get checked for iron, thyroid, vitamin D, and ferritin first, these are far more common drivers than biotin.
• Why pause biotin before lab tests?+

  Biotin at doses above 5 mg per day can interfere with the immunoassay technology used for thyroid hormones, troponin (heart attack marker), parathyroid hormone, vitamin D, and many other tests, producing misleading results. The FDA has issued safety communications. Pause for at least 72 hours before lab work and tell your clinician and the lab any biotin you take.
• Is high-dose biotin safe?+

  Toxicity is essentially unreported even at very high doses (over 100 mg per day in genetic deficiency treatment), but assay interference is a real and underappreciated risk. The supplement itself is safe; the consequences of a missed heart attack diagnosis or a wrong thyroid treatment decision because of skewed labs are not. Use low doses when high doses are not needed.
• Do I need biotin if I take a B-complex?+

  A standard B-complex provides 30 to 300 mcg of biotin, well above the adequate intake. Adding a separate high-dose biotin on top is rarely necessary and increases the risk of assay interference. Use a single B-complex unless you have a specific high-dose indication.
• Does it matter if I take Biotin at a different time each day?+

  Some variation is fine. A fixed slot is recommended mainly because it is the easiest way to not forget, and because it keeps levels of quickly cleared compounds steadier. Drifting an hour or two either side of your usual time changes very little. Drifting between morning and bedtime is worth avoiding, especially if Biotin affects your sleep or energy.
• Can I take Biotin twice a day instead?+

  Splitting a dose is often better tolerated and, for compounds the body clears quickly, keeps blood levels steadier than one large dose. Do not increase the total by splitting it: divide the daily amount you were already taking. Check the label, some products are formulated as a single daily dose and should not be split.

• FDA Safety Communication, Biotin Interference