L-Methionine
Also called L-methionine, methionine, methionine supplement, L-methionine 500 mg.
Best grade C across 6 graded outcomes Amino acid Last checked
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The short answer
From 10 sourcesL-methionine is an essential sulfur amino acid sold in 500 mg capsules. In a 20-woman crossover trial, 1,500 mg a day for 4 weeks raised plasma homocysteine by about 2 µmol/L despite adequate B vitamins. Hospitals have used methionine as a paracetamol-overdose antidote, and urologists use it to acidify urine; neither is self-care.
Every graded outcome on this page
6 rows · line = participants- CGrade CCD4 count decline in HIV infectionImmune functionn 253
- DGrade DFlow-mediated dilation after a methionine loadBlood vesselsn 24
- DGrade DPlasma homocysteineHomocysteinen 20
- DGrade DBlood-vessel function and homocysteineBlood vesselsn 16
- DGrade DCysteine and glutathione productionGlutathionen 12
- DGrade DStone and infection recurrence with urine acidificationUrinary stonesn 8
- 3 more graded outcomes, in the evidence chapter
Key facts
- What it is
- An essential sulfur amino acid; homocysteine is formed as it is broken down1
- Homocysteine (20 women)
- 1,500 mg a day for 4 weeks raised plasma homocysteine by about 2.0 µmol/L vs placebo1
- Low dose
- 250 mg a day for a month did not change homocysteine or blood-vessel function in 16 adults2
- Methionine load
- A single 0.1 g/kg dose tripled homocysteine and halved flow-mediated dilation within 4 hours3
- Label dose
- A common label serving is 1,000 mg (2 × 500 mg) with 20 mg vitamin B67
- Loading-test tolerance
- In 350 people given a diagnostic methionine load, 22.1% had mild to moderate symptoms, mostly nausea that passed after breakfast10
What it is
L-methionine is an essential sulfur amino acid; as a supplement, its best-documented effect is a rise in blood homocysteine.
Forms
Form
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| L-methionine (free form) capsules | Varies1Not applicable; doses are mg of L-methionine | Serum methionine rose from 33.0 to 53.6 µmol/L on 1,500 mg a day vs placebo, and urinary methionine and homocysteine rose.1 | No vessel-function harm at 250 mg a day; at 1,500 mg a day homocysteine rose.12 | Homocysteine, blood-vessel function, urine acidification |
What the human research says
Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.
Trial map
6 graded outcomes, largest study first6 graded outcomes: 1 improved, 2 mixed, 1 no effect, 2 worsened. The largest, a 2007 randomized trial of 253 people on CD4 count decline in HIV infection, found mixed results. 2 outcomes found a worsening: Flow-mediated dilation after a methionine load (24 people) and plasma homocysteine (20).
1CD4 count decline in HIV infection
Mixed · Grade C · RCT, 253 people, 2007
People with HIV at four trial centres
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| CD4 count decline in HIV infection | Mixed | 253 | Grade C · RCT, 2007 | People with HIV at four trial centres |
| Flow-mediated dilation after a methionine load | Worsened | 24 | Grade D · Crossover RCT, 1998 | Healthy adults |
| Plasma homocysteine | Worsened | 20 | Grade D · Crossover RCT, 2005 | 8 women with chronic urinary tract infection and 12 healthy women |
| Blood-vessel function and homocysteine | Mixed | 16 | Grade D · Open-label trial, 1999 | Healthy volunteers |
| Cysteine and glutathione production | No effect | 12 | Grade D · RCT, 2014 | Children with edematous severe acute malnutrition in hospital |
| Stone and infection recurrence with urine acidification | Improved | 8 | Grade D · Observational, 2026 | Adults aged 26 to 77 with infection stones, brushite stones or dystrophic calcification |
Every graded row
6 rowsShowing 6 of 6 outcomes. Human trials only.
CGrade CCD4 count decline in HIV infectionImmune functionSlower CD4 decline in subgroupsRCT
n 253 · 2007
Mixed After six months, CD4 counts declined less on L-methionine than placebo in women (p = 0.0027) and at one of the four centres (p = 0.0377); the abstract reports similar tendencies in the whole group without statistics. No serious side effects were linked to treatment.
- Design
- RCT, n = 253, 2007
- Population
- People with HIV at four trial centres
- Form
- L-methionine
- Dose
- Not stated in the abstract
- Duration
- 12 months randomized (results reported at 6 months), then open-label follow-up to 48 months
- Source
- Reference 9 · PubMed 17006600 (opens PubMed)
DGrade DFlow-mediated dilation after a methionine loadBlood vesselsWorse vessel dilationCrossover RCT
n 24 · 1998
Worsened Homocysteine rose from 7.9 to 23.1 µmol/L at 4 hours and flow-mediated brachial dilation fell from 0.12 to 0.06 mm (p < 0.05), mirroring the homocysteine curve.
- Design
- Crossover RCT, n = 24, 1998
- Population
- Healthy adults
- Form
- Oral methionine load
- Dose
- 0.1 g per kg of body weight, once
- Duration
- Single dose, measured over 4 to 8 hours
- Source
- Reference 3 · PubMed 9799203 (opens PubMed)
DGrade DPlasma homocysteineHomocysteineHigher homocysteineCrossover RCT
n 20 · 2005
Worsened Homocysteine rose from 9.4 to 11.2 µmol/L in patients and from 8.9 to 11.0 µmol/L in controls vs placebo, with higher serum methionine and cystathionine, despite adequate vitamin B12, B6 and folate status.
- Design
- Crossover RCT, n = 20, 2005
- Population
- 8 women with chronic urinary tract infection and 12 healthy women
- Form
- L-methionine (free form)
- Dose
- 500 mg three times a day (1,500 mg/day)
- Duration
- 4 weeks
- Source
- Reference 1 · PubMed 15870821 (opens PubMed)
DGrade DBlood-vessel function and homocysteineBlood vesselsHomocysteine up only at high doseOpen-label trial
n 16 · 1999
Mixed Endothelium-dependent vasodilation did not change at any dose. Homocysteine did not change at 250 mg a day but rose significantly on 100 mg/kg a day.
- Design
- Open-label trial, n = 16, 1999
- Population
- Healthy volunteers
- Form
- L-methionine
- Dose
- 250 mg once; 250 mg a day; 100 mg/kg a day
- Duration
- Single dose, 1 month (low dose) or 1 week (high dose)
- Source
- Reference 2 · PubMed 10465239 (opens PubMed)
DGrade DCysteine and glutathione productionGlutathioneNo changeRCT
n 12 · 2014
No effect Methionine sped cysteine release from body protein but did not change cysteine synthesis or red-cell glutathione synthesis.
- Design
- RCT, n = 12, 2014
- Population
- Children with edematous severe acute malnutrition in hospital
- Form
- Methionine vs alanine (control)
- Dose
- 0.5 mmol per kg a day
- Duration
- About 1 week, measured with stable-isotope tracers
- Source
- Reference 4 · PubMed 24598154 (opens PubMed)
DGrade DStone and infection recurrence with urine acidificationUrinary stonesFewer recurrences (case reports)Observational
n 8 · 2026
Improved With urinary pH monitored, stones did not recur or regrow after surgery in the six infection-stone cases, and infection did not recur.
- Design
- Observational, n = 8, 2026
- Population
- Adults aged 26 to 77 with infection stones, brushite stones or dystrophic calcification
- Form
- L-methionine with phytate
- Dose
- Not stated in the abstract
- Duration
- Not stated in the abstract
- Source
- Reference 5 · PubMed 42803672 (opens PubMed)
What the numbers add up to
Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.
Studied doses
Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.
Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.
Doses studied in human trials
Interactions and safety
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
What L-Methionine meets
0 cited rows 1 tested togetherMedicines 0
No medicine rows in our sources.
Supplements and foods 1
- Tested together in a graded trial
Choose a medicine or supplement above to read its cited rows here.
Also cited: 1 tested together
IP6IP6 page
Tested together
Stone and infection recurrence with urine acidification. Graded on the L-Methionine page; tested together is not a claim that they work better together.
Interactions
0 agentsNone found in our sources.
Check with what you take
Kept on this device onlyAdd what you take. We list every interaction our evidence profiles cite between L-Methionine and your picks, and between your picks.
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Add a supplement or medicine you take to check it against L-Methionine.
Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.
Who should be careful
4 groups- High homocysteine or heart risk
- 1,500 mg a day raised plasma homocysteine by about 2 µmol/L even with adequate B vitamins, and the label warns it may raise homocysteine.17
- Pregnancy, breastfeeding, medicines
- The label says adults only and to consult a physician if pregnant or nursing, taking medication or having a medical condition.7
- Paracetamol overdose
- Methionine has been tested as a hospital antidote for paracetamol overdose; an overdose is an emergency, not something to manage with a supplement.6
- Medicines and surgery
- NCCIH advises telling your health care providers about every supplement you use.8
How to read the label
What to check on the Supplement Facts panel.
How to read the label
1 checksWhere to buy L-Methionine
Products from brands we partner with that contain L-Methionine. Check the amount per serving against the doses studied above, and the label for other ingredients.
L-Methionine products from partner brands
1 product Paid links · we earn a commission- HerbsProNOW Foods L-Methionine 500 mg, 100 capsules
500 mg L-methionine per capsule; the label serving is 2 capsules (1,000 mg) with 20 mg vitamin B6, and the label warns it may raise homocysteine
$14.99one-timeChecked Oct 17, 2026
Frequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
6 answersDoes L-methionine raise homocysteine?
Does L-methionine help with urinary stones?
Only case reports exist: eight patients given L-methionine with phytate under urinary pH monitoring had no stone recurrence after surgery. No controlled trial was found.5
Does methionine raise glutathione?
In 12 malnourished children, methionine sped cysteine release from body protein but did not change glutathione synthesis vs alanine.4
Is methionine used for paracetamol overdose?
Hospitals have used it as an antidote. A Cochrane review found acetylcysteine's superiority over methionine unproven; either way, overdose needs emergency care.6
What are the side effects of L-methionine?
Small supplement trials report little on side effects; the main measured change was higher homocysteine at 1,500 mg a day. In 350 people given a large diagnostic methionine load, 22.1% had mild to moderate symptoms, mostly nausea that passed after breakfast, and some had dizziness or blood-pressure changes.110
Sources
10 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
10 sources- 1Effect of L-methionine supplementation on plasma homocysteine and other free amino acids: a placebo-controlled double-blind cross-over study.Crossover RCT Eur J Clin Nutr, 2005 · PMID 15870821
- 2Effect of methionine supplementation on endothelial function, plasma homocysteine, and lipid peroxidation.Open-label trial J Toxicol Clin Toxicol, 1999 · PMID 10465239
- 3Hyperhomocysteinemia after an oral methionine load acutely impairs endothelial function in healthy adults.Crossover RCT Circulation, 1998 · PMID 9799203
- 4Effects of randomized supplementation of methionine or alanine on cysteine and glutathione production during the early phase of treatment of children with edematous malnutrition.RCT Am J Clin Nutr, 2014 · PMID 24598154
- 5Phytate and L-methionine for preventing recurrence of infection renal stones.Observational Arch Ital Urol Androl, 2026 · PMID 42803672
- 6Interventions for paracetamol (acetaminophen) overdose.Meta-analysis Cochrane Database Syst Rev, 2018 · PMID 29473717
- 7NOW Foods L-Methionine 500 mg, 100 capsules: Supplement Facts and warnings (read 2026-10-17)Label HerbsPro product page, 2026 · herbspro.com
- 8Using Dietary Supplements WiselyFact sheet National Center for Complementary and Integrative Health (NCCIH), 2019 · nccih.nih.gov
- 9L-methionine as immune supportive supplement: a clinical evaluation.RCT Amino Acids, 2007 · PMID 17006600
- 10Safety of the oral methionine load test: effects on the clinical performance and laboratory tests.Observational Rev Invest Clin, 2013 · PMID 24304733
What changed
Every dated change to this page: what changed, who made it and why.
Change log
2 entries| Date | Change | Who and why |
|---|---|---|
| evidence, key facts, FAQ, questions, related | Added a row for the largest randomized L-methionine trial (2007, 253 people with HIV; slower CD4 decline only in subgroups, dose not stated, grade C), a 350-person study of tolerance of the diagnostic methionine load (22.1% mild to moderate symptoms, mostly nausea), FAQ items on side effects and long-term safety, page questions and a goal-hub link. PubMed search for L-methionine meta-analyses and RCTs through 2026 found no newer supplement trial on homocysteine or vessel function; the newer hits were SAMe, D-methionine or methionine-restriction studies. Interactions checked: LiverTox, LactMed and NCCIH have no methionine entry and MedlinePlus no longer has a methionine monograph, so the list stays empty; an older report of methionine weakening levodopa could not be located in PubMed and was not added. | Writer: Kymata Health EditorialTrigger: A–Z audit against docs/supplements/AUDIT-STANDARD.md |
| all | Initial editorial evidence review. Every PMID checked against NCBI E-utilities esummary (title, year, journal) and each cited abstract read; numbers taken from the abstracts. The homocysteine rise is shown as a worsened outcome; loading-test and hospital antidote data are labelled as such. Where to buy: NOW Foods L-Methionine 500 mg (checked 2026-10-17), label facts only. | Writer: Kymata Health EditorialTrigger: new page |
Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.