Methionine
DL-Methionine, Racemethionine
Also known as: Ammonil · Acimethin · Acimol · M-Caps · Methigel · Methio-Form · Methiotrans · Methnine · Neutrodor · Pedameth · Uracid · Uromethin · Uroeze · dl-methionine · racemethionine · s-methionine · methioninum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Urine acidification (struvite dissolution) | 100 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Struvite dissolution therapy (if diet and antimicrobials do not result in acid urine) | 0.2-1 gram PO q8h | PO | q8h | — | 🌎 NA |
- Urine acidification (struvite dissolution): Safe and effective in dissolving presumed infection-induced struvite uroliths in combination with an appropriate anti-microbial agent without using a struvite dissolution diet.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Urine acidification | 1000-1500 mg per day given in the food once daily | PO | q24h | — | 🌎 NA |
| Urine acidification | 0.2-1 gram PO once daily | PO | q24h | — | 🌎 NA |
- Urine acidification: Use if diet and antimicrobials do not reduce pH.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Laminitis (purported) | 22 mg/kg PO once daily for one week; then 11 mg/kg PO once daily for 1 week; then 5.5 mg/kg PO once daily for one week | PO | q24h | 3 weeks | 🌎 NA |
| Senecio-induced liver damage | 12.5 grams IV in one liter saline/dextrose solution | IV | Once | — | 🌎 NA |
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General / Ketosis | 20-30 grams PO | PO | — | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Methionine is a sulfur-containing essential amino acid used primarily in veterinary medicine as a urinary acidifier and nutritional supplement.
- Urinary Acidification: Historically used to dissolve and prevent struvite (magnesium ammonium phosphate) uroliths by lowering urine pH.
- Clinical Pearl: Its use in small animals has largely been superseded by specialized prescription urinary diets (e.g., s/d, c/d) that effectively manage urine pH without the need for additional supplementation.
- Lipotropic Agent: Acts as a lipotrope to prevent or correct fatty liver in choline-deficient states.
- Large Animal Use: Used as a nutritional supplement in swine and poultry, for the treatment of ketosis in cattle, and purportedly for laminitis in horses and cattle (theorized to provide a disulfide bond substrate to maintain the hoof-pedal bone bond), though definitive efficacy for laminitis is lacking.
Mechanism of action
Methionine exerts its effects through several metabolic pathways:
- Urine Acidification: Methionine is metabolized in the liver, where its sulfur component is oxidized to sulfate. This sulfate is excreted by the kidneys as sulfuric acid → effectively lowering urine pH.
- Lipotropic Action: Methionine supplies methyl groups to ethanolamine → forms choline, which is essential for lipid transport and metabolism in the liver, preventing hepatic lipidosis.
- Antioxidant & Structural Precursor: Two molecules of methionine convert to one molecule of cysteine, a critical precursor for glutathione (a major endogenous antioxidant) and essential for disulfide bond formation in structural proteins (like keratin in hooves).
Safety & warnings
Contraindications
- Renal failure
- Pancreatic disease
- Hepatic insufficiency
- Preexisting acidosis
- Oxalate or urate calculi
- Kittens
- Pre-existing metabolic acidosis
- Severe liver disease or hepatic encephalopathy
- Urate, cystine, or calcium oxalate urolithiasis
- Young growing animals
- Pregnant or nursing animals
Adverse effects
- Gastrointestinal distress (nausea, vomiting)
- Heinz-body hemolytic anemia (especially in cats)
- Methemoglobinemia
- Ataxia
- Cyanosis
- Metabolic acidosis
- Gastrointestinal upset (nausea, vomiting, diarrhea)
- Heinz body anemia (especially in cats at high doses)
- Worsening of hepatic encephalopathy in patients with liver disease
Precautions
Hepatic Warning: If used in patients with frank hepatic insufficiency, methionine can cause increased production of mercaptan-like compounds and intensify the signs of hepatic encephalopathy (dementia or coma).
- Urolithiasis Risk: Do not give to animals with oxalate or urate calculi, as these stones thrive in acidic environments.
- Dietary Overlap: Unmonitored use concurrently with an acidifying diet (e.g., s/d, c/d) may easily lead to severe metabolic acidosis and signs of overdose.
- Age Restrictions: Strictly not recommended for use in kittens due to high susceptibility to toxicity.
Drug interactions
Urine acidification may diminish the effectiveness of aminoglycosides in treating bacterial urinary tract infections, as they are more effective in an alkaline medium.
Urine acidification may diminish the effectiveness of erythromycin in treating bacterial urinary tract infections.
Urine acidification may increase the renal excretion of quinidine, potentially lowering its systemic levels.
Additive acidification leading to severe metabolic acidosis
Excessive lowering of urine pH and increased risk of metabolic acidosis
Monitoring
- Urine pH (goal of therapy is typically ≤6.5)
- Blood pH (if signs of toxicity or metabolic acidosis are present)
- CBC in cats (if exhibiting signs of toxicity, to check for Heinz-body anemia)
- Complete Blood Count (CBC) to monitor for Heinz bodies, especially in cats
- Acid-base status (blood gases) if overdosage is suspected
- Liver function
Pharmacokinetics
Half-life
Absorption
Well absorbed from the gastrointestinal tract.
Distribution
Widely distributed throughout the body tissues as it is an essential amino acid.
Metabolism
Metabolized in the liver to sulfate and urea.
Elimination
Excreted primarily by the kidneys into the urine.
Overdose
Feline Toxicity: Cats are particularly sensitive to methionine overdose.
- When administered at a dose of 2 grams orally per day to mature cats, it caused anorexia, methemoglobinemia, Heinz body formation (with resultant hemolytic anemia), ataxia, and cyanosis.
- Kittens: Methionine may be highly toxic to kittens who consume other cats' food to which methionine has been added.
General Toxicity: Metabolic acidosis can occur with overdoses in any species, particularly when used in combination with an acidifying diet. No specific information was located on the treatment of methionine overdosage; treatment should be symptomatic and supportive (e.g., correcting acid-base imbalances).
Available products
Formulations
- Chewable tablets
- Oral powder
- Oral gel
- Capsules
- Topical ointment, cream, lotion, pads
- Oral: 500 mg tablets
Veterinary
- Methionine Tablets: 200 mg and 500 mg (Ammonil®, DL-Methionine Tablets®)
- Methionine Chewable Tablets: 500 mg (Methio-Form®)
- Methionine Powder (d-l-methionine Powder)
- Methionine Gel: 400 mg (8%) per 120.5 gram tube (Methigel®)
- 500 mg tablets (General Sale)
Human-labeled
- Methionine Capsules: 500 mg
- Topical Ointments, cream, lotion, pads and powder
- Various OTC dietary supplements (typically 500 mg capsules/tablets)
Regulatory status
Available as a general sale item.
Classified as general sale.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Methionine should be stored at room temperature.
Client information
- Administration: Give this medication with meals or mixed directly into your pet's food to reduce stomach upset and enhance effectiveness.
-
Important Warning: Do not give to kittens, and ensure kittens cannot access adult cat food that has been treated with this medication.
- Dietary Caution: Do not combine this medication with prescription urinary diets (like s/d or c/d) unless specifically instructed by your veterinarian, as this can cause dangerous changes in blood acid levels.
- When to Call the Vet: Contact your veterinarian immediately if your cat shows signs of weakness, loss of appetite, uncoordinated walking, or pale/bluish gums.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.