Best-documented harm is dose-dependent GI intolerance — bloating, gas and an osmotic/laxative effect, typically above ~20-50 g/day (individuals vary), which is why labels carry laxative warnings. Xylitol is acutely TOXIC TO DOGS (and ferrets): doses >0.1 g/kg can cause life-threatening hypoglycemia and >0.5 g/kg acute liver failure — the FDA has issued a specific consumer warning to keep gum, candy and sugar-free peanut butter away from pets. The emerging human signal is cardiovascular: Witkowski et al. (European Heart Journal 2024) found that people in the highest tertile of fasting plasma xylitol had ~1.5-fold higher 3-year risk of major adverse cardiovascular events, and showed in human and animal experiments that ingesting ~30 g enhanced platelet reactivity and clotting. This is an association plus mechanism, not proof of causation; confounding (xylitol is endogenously produced and tracks with cardiometabolic status), measurement of circulating vs ingested xylitol, and lack of RCT outcome data mean it should be treated as a signal under active study, not an established harm. Dental-caries benefit is real but modest and rests on low-to-very-low-quality evidence (Cochrane 2015). People with cardiovascular risk who consume large daily amounts may reasonably moderate intake pending confirmation; the general no-calorie/dental use at typical levels has a long safety record. Educational only — always check with your doctor or pharmacist before combining Xylitol with any medicine.