Aspirin is an NSAID (nonsteroidal anti-inflammatory drug). Because of its anti-inflammatory properties, it is often used to treat arthritis, toothaches, and other pains aggravated by inflammation. It is also used to treat minor body aches and pains, headaches, and reduce fevers. Aspirin has two major side effects. The first is that it can be stomach irritant. In fact, it can irritate any tissue it comes into contact with (thus chewing aspirin gum is not recommended because it can irritate the gums and mouth).