{"ok":true,"entry":{"slug":"l-serine","kind":"supplement","name":"L-serine","aliases":["serine"],"brands_sg":["California Gold Nutrition","Nutricost","NOW Foods","Vitamatic","Double Wood Supplements"],"class":"amino acid","tags":["cognitive","sleep"],"use_for":"limited human evidence — circadian timing, rare genetic use","use_after":"in the trial, 3 g went 30 min before bedtime","use_duration":null,"take_with":null,"pros":["one small trial: 3 g at night held circadian phase","52-week use in one patient: no direct side effects","not named in HSA's prohibited or restricted annexes"],"cons":["not in HSA's vitamin/mineral tables — no SG cap","human trials are tiny — 33 students, single patients","the sleep tag rests on one circadian-phase study"],"dose_note":"the circadian study used 3.0 g 30 min before bedtime for 2 weeks; a single-patient neuropathy report titrated to 400 mg/kg/day under medical supervision","dosage":{"ul":null,"unit":"g","fda_dv":null,"rda_ai":null,"ul_status":"none_established","population":"general adult","hsa_max_daily":null},"ul_status":"none_established","sg_class":null,"cautions":["rare-neuropathy dosing was medically supervised","no upper limit set anywhere — absence of a cap is not safety"],"clashes":[],"sources":[{"id":"ohashi2022","url":"https://europepmc.org/article/PMC/PMC9413878","label":"Intake of L-serine before bedtime prevents the delay of the circadian phase in real life (Ohashi et al., J Physiol Anthropol 2022)","quote":"the subjects took 3.0 g of L-serine or a placebo 30 min before bedtime for 2 weeks … DLMO after intervention was significantly delayed … in the placebo group (p = 0.02) but not in the L-serine group","accessed":"2026-08-27"},{"id":"auranen2017","url":"https://europepmc.org/article/PMC/PMC5701299","label":"Clinical and metabolic consequences of L-serine supplementation in HSAN1C (Auranen et al., Cold Spring Harb Mol Case Stud 2017)","quote":"a 52-wk treatment in which the L-serine dose was titrated up to 400 mg/kg/day … There were no direct side effects from the treatment, but the patient developed a transitory toe ulceration","accessed":"2026-08-27"},{"id":"hsa_pr","url":"https://file.go.gov.sg/hsa-chp-prohibited-restricted-ing-guidelines.pdf","label":"HSA — Guidelines on prohibited and restricted ingredients in HS and TM (Oct 2025), Annex A","quote":"Annex A: List of substances which are prohibited or restricted for use with … [serine is not listed among the 100+ named entries]","accessed":"2026-08-27"},{"id":"hsa_hs","url":"https://file.go.gov.sg/hsa-hs-guidelines.pdf","label":"HSA — Health Supplements Guidelines (Jan 2026), Tables 4–5 vitamin and mineral limits","quote":"Table 4: Vitamins Limits … Table 5: Minerals Limits [neither table names serine; the limits cover named vitamins and minerals only]","accessed":"2026-08-27"},{"id":"iherb_sg","url":"https://sg.iherb.com/c/l-serine","label":"iHerb Singapore — l-serine category page (default best-selling order)","quote":"California Gold Nutrition · Nutricost · NOW Foods · Vitamatic · Double Wood Supplements [first distinct brands, default order]","accessed":"2026-08-27"}],"brand_certs":null,"updated_at":"2026-08-29T16:16:23.779398+08:00"},"disclaimer":"kozen-x is not a medical device and does not give medical advice. it lists what published sources have written down. absence of a record is not the same as safe."}