Phenolphthalein is a chemical compound that is commonly used as an acid-base indicator in laboratory experiments. However, it is harmful if ingested. If someone drinks phenolphthalein, it can cause irritation of the digestive tract, fever, blood pressure increase, and other unspecified vascular effects. Large doses of phenolphthalein can cause nausea, vomiting, and diarrhea. Phenolphthalein is also a strong laxative, and ingestion of even small quantities of phenolphthalein or its solutions will purge most people. In most people, ingested phenolphthalein can cause diarrhea but no other problems. If someone drinks phenolphthalein, they should seek medical attention immediately.