Calcium supplements often come in chewable (e.g., chocolate-flavored) or tablet formulation in human medicine, and are readily found in households. When dogs ingest these supplements in large amounts, it can result in electrolyte changes (e.g., transiently elevated calcium blood levels) or even chocolate poisoning in dogs. (Cats, by the way, generally do not ingest enough of these supplements to result in poisoning due to their discriminating palate.) Calcium supplements often also contain large amounts of Vitamin D3 and Vitamin K, which can also result in toxicity. While calcium is generally poorly absorbed from the gastrointestinal tract, the addition of Vitamin D3 increases the risk of toxicity.
Calcium supplements, when ingested, generally are safer than other types of Vitamin D (e.g., cholecalciferol, calcipotriene), which can be deadly. Clinical signs of poisoning include nausea, vomiting, diarrhea, excessive thirst or urination, weakness, acute kidney failure, and tremors.
If you suspect your dog or cat were poisoned by calcium, call your veterinarian or Pet Poison Helpline immediately for treatment advice.