Despite serious safety concerns, pennyroyal is used for colds, pneumonia, and other breathing problems. It is also used for stomach pains, gas, intestinal disorders, and liver and gallbladder problems. Women use it to start or regulate their menstrual periods, or to cause an abortion. Pennyroyal is also used to control muscle spasms, cause sweating, and increase urine production. Some people use it as a stimulant and to counteract weakness.

In foods, pennyroyal is used for flavoring. In manufacturing, pennyroyal oil is used as a dog and cat flea repellent; and as a fragrance for detergents, perfumes, and soaps.

If you are pregnant or breast-feeding, it is LIKELY UNSAFE to take pennyroyal by mouth or apply it to your skin. Pennyroyal leaf tea seems to be able to start menstruation, which could also threaten a pregnancy. It is LIKELY UNSAFE to give children pennyroyal by mouth. The oil in pennyroyal can irritate the kidney and make existing kidney disease worse. The oil in pennyroyal can cause liver damage and might make existing liver disease worse.