Cucurbitacin
Normally, the amount of Cucurbitacin is low, but if you taste "bitterness" don't eat to much, as it can in specific situations be dangerous to your health.
Deaths
After examining the body of a 79-year-old man who died in Bavaria, Germany, the "Chemische- und Veterinäruntersuchungsamt Stuttgart" (chemical and veterinary research authority) found cucurbitacin in a sample of a home-grown zucchini the man had eaten shortly before his death. According to the report, the poison was also found in the stomach of the man, who died in the hospital shortly after eating the zucchini. He had been given the plant by a neighbor.