L-Methionine: Douglas Laboratories®

L-methionine is an essential amino acid, meaning it must be supplied in the diet to maintain health. When given as a supplement, it can act as a natural urinary acidifier. This means it will make the urine more acidic or lower the urine pH.

L-Methionine is intended to acidify urine in cats that have chronic cystitis (FUS, FLUTD); it is the natural form of methionine, not the synthetic dl-Methionine.

L-methionine is NOT the more commonly used dl-methionine, which is a synthetic product. For most animals, we like the more gentle acidifying effect of l-methionine over the synthetic compound.

Not all animals should have their body acidified, and this product is primarily intended for cats or dogs with struvite or triple phosphate stones.

Many dogs and cats can have their struvite stones controlled by diets and supplementing with our Chinese herbal formula Cystitis and Dissolve Stone Formula (only available after a phone consultation). To more natural acidify the urine, you can also alter the diet to include much higher amounts of meat/protein in the diet. Increasing the protein will cause a more acidic urine. See our articles on Feeding Your Dog and Feeding Your Cat for more information on diets.

We also have articles on feeding your cat or dog a home cooking diet that is intended for dogs and cats with Struvite stones. We have an article on feeding animals with struvite stone on this web site.


Cats and dogs with Struvite or Triple Phosphate stones or crystals can develop cystitis or bladder inflammation. If the stones are moderately small, they can travel into the urethra, plugging it up; the result is that your companion can no longer urinate. Larger stones can fill up the bladder, a very painful problem indeed.

Some urinary crystals are normal and of no problem. Consistent production of larger amounts of crystals can lead to their formation into stones and the resulting problems with cystitis and obstruction of urine flow. Struvite crystals can not develop if the urine is acidic (a low pH). Diet modification to one with higher meat or protein will acidify the urine. If this is not enough, we recommend adding the naturally occurring l-methionine. If the urine is still not acidic, then we recommend adding the synthetic dl-methionine.


  • Use in cats with FLUTD, FUS, and Struvite stones
  • Use in dogs with chronic production of struvite crystals in the urine
  • Use in dogs with Triple Phosphate stones and Struvite stones to help dissolve the stones
  • Use in cats with Cystitis


The best way to dose this product is to purchase pH test strips from a pharmacy and check your animal's urine pH regularly. You will want to have a pH between 6.0 and 7.0, while 6.5 is probably ideal. Immediately after eating, the pH will rise (become more alkaline, or above 7.0). If the urine does not stay alkaline for more than a few hours each day, you are dosing methionine correctly.

Place in food at the rate of 1/4 capsule per meal for each 15 lbs body weight. Increase the dosage as needed until the pH is consistently below 7.0.

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