Updated July 2021

Beginning in the 1990s, veterinarians began seeing dogs who developed acute kidney failure after eating grapes, raisins, or currants. The cause has been a total mystery for decades. But in 2021, tartaric acid (which cream of tartar is made from) was discovered to be the part of grapes that cause them to be toxic to pets. The amount of tartaric acid can vary in grapes by their type, how they were grown, and how ripe they are, which could explain why some pets get very sick while others seem unaffected after eating similar amounts of grapes or raisins.  There is still a lot of research and work still to do, but here’s more on this new hypothesis.

While chronic kidney disease (CKD) is commonly seen in older cats and dogs, it is usually due to a chronic, low-grade, inflammatory process called glomerulonephritis. Recent research suggests that, in cats, contributing factors may include consumption of fish, and the vaccine for panleukopenia (feline distemper). (Click here for more info on CKD in cats.) In contrast, dogs who developed grape/raisin toxicity were found to have damage and even necrosis (tissue death) in the proximal renal tubular epithelium, which is a different location in the kidney. Grape/raisin toxicity causes signs of illness within hours, and kidney failure develops within days; as opposed to the gradual development of chronic kidney disease over many months or years.Signs of acute grape/raisin/currant toxicity include vomiting, diarrhea, lethargy, loss of appetite, increased drinking and urination, and dehydration. Grape/raisin/currant toxicity has been documented only in dogs, although there have been anecdotal reports of a similar problem in cats and ferrets.

Readers have asked about the issue of grape/raisin toxicity in dogs, and what it means for the Chardonnay grape seed oil in the Omega-3 supplement MOXXOR. After thoroughly researching this issue, we have concluded that:

  • Tartaric acid appears to be the toxic factor, but levels in grapes vary greatly depending on variety, growing conditions, and processing factors.
  • The toxic reaction appears to occur in only individuals with a particular susceptibility. However, whether that susceptibility is genetic or otherwise is yet unknown.
  • The grape seed oil in MOXXOR is from Chardonnay grapes. There have been no reports of toxicity in dogs related to that type of grape.
  • The toxic dose of raisins in dogs is typically about 1/2 ounce of raisins, or 3 ounces (85 grams) of fresh grapes (about 17 small grapes, or 1/2 cup), per 10 lb. of body weight. One grape weighs about 7 grams.
  • There are 28 grams in an ounce; and there are five MOXXOR capsules in 1 gram. The grape seed oil used as an antioxidant comprises only a tiny fraction of the 350 mg of oil in the capsule. The actual amount of grape seed oil is miniscule compared to the toxic dose range, so it is impossible for a reaction to occur even with higher doses of MOXXOR.

We are, therefore, 100% comfortable with recommending MOXXOR for any species.