“DL-Methionine?”Here!

Synthetic

Hasn’t appeared in a scanned product yet.

As a supplement

Talk to your doctor or pharmacist.

Roll Call does not check drug interactions or assess personal safety.

A racemic mixture of the essential amino acid methionine, combining its D- and L- mirror-image forms. The L-form is the one the body normally uses to build proteins.

Why it’s used

Taken by some as a general amino acid or antioxidant-support supplement, and sometimes included in products marketed for liver support or odor control.

What the evidence says

NIH ODS does not maintain a fact sheet on DL-methionine as an oral supplement for general health. Methionine's biochemical role in protein synthesis and one-carbon metabolism is well established, but there is little clinical trial evidence for benefits from supplementing beyond correcting a dietary deficiency, which is uncommon in typical diets.

Where we looked

There was no paper to cite here, so this is the search instead — run it yourself and see what we saw.

PubMed: 73 records · searched September 2026"DL-Methionine"[Title/Abstract] AND (review[pt] OR "safety assessment"[Title/Abstract] OR "risk assessment"[Title/Abstract] OR toxicology[Title/Abstract] OR toxicity[Title/Abstract] OR characterization[Title/Abstract] OR characterisation[Title/Abstract])
PubMed: 2 records · searched September 2026"DL-Methionine"[Title/Abstract] AND ("dietary supplements"[MeSH] OR supplementation[Title/Abstract] OR supplement[Title/Abstract] OR supplements[Title/Abstract] OR "oral administration"[Title/Abstract]) AND (randomized controlled trial[pt] OR clinical trial[pt] OR meta-analysis[pt] OR systematic review[pt]) AND humans[MeSH]
PubMed: 793 records · searched September 2026"DL-Methionine"[Title/Abstract]

This says what this database holds under these terms. It is not a finding that no research exists.

Context

No consistent dosing protocol appears across the limited human research.

Rumors

1
DL-methionine is toxic to kittens and stunts their growth.
Supports — suggestivehealth and safety evidence
Studied in: kittens.
Measured as an outcome.
- Effect of excess dietary methionine on weight gain and plasma amino acids in kittens (Peer-reviewed) · Funding not checked
Who’s saying this
- PetMD — a publisher: pet health information
  How we know who this is
  “PetMD is the online authority for all things pet health.” (their page)
2
DL-methionine treats and prevents struvite bladder stones in dogs and cats by acidifying the urine.
Supports — suggestivehealth and safety evidence
Studied in: clinically normal cats fed dry food.
Measured as a biomarker.
- Effect of supplementation of dry cat food with D,L-methionine and ammonium chloride on struvite activity product and sediment in urine (Peer-reviewed) · Funding not checked
- Controlling Urine pH in Animals - Pharmacology - Merck Veterinary Manual (Database) · Funding not checked
Who’s saying this
- PetMD — a publisher: pet health information
  How we know who this is
  “PetMD is the online authority for all things pet health.” (their page)
3
DL-methionine helps repair the liver and detoxify the body.
We haven’t found evidence strong enough to support this or rule it out.
What was measured is not yet noted.
Who’s saying this
- dogster.com — we couldn’t open the site to see who runs it
4
DL-methionine strengthens weak, cracking horse hooves.
We haven’t found evidence strong enough to support this or rule it out.
What was measured is not yet noted.
Who’s saying this
- Mad Barn — a brand: sells horse nutrition supplements
  How we know who this is
  “Mad Barn products are formulated with research-backed ingredients and designed to support a balanced diet for all horses.” (their page)
5
DL-methionine supports strong, healthy hair.
We haven’t found evidence strong enough to support this or rule it out.
What was measured is not yet noted.
Who’s saying this
- BulkSupplements.com — a brand: sells nutritional supplement ingredients
  How we know who this is
  “Located in Henderson, Nevada, BulkSupplements.com supplies over 500 pure nutritional supplement ingredients to hundreds of thousands of consumers and manufacturers.” (their page)