Aspirin is a commonly used medication that can cause several side effects, including: Stomach problems: Aspirin can irritate the stomach lining, causing nausea, vomiting, indigestion, heartburn, and stomach pain. Bleeding: Aspirin can increase the risk of bleeding, including stomach bleeding, brain bleeding (hemorrhagic stroke), and heavy menstrual bleeding. Allergic reactions: Some people may have an allergic reaction to aspirin, including hives, itching, rash, and difficulty breathing. Tinnitus (ringing in the ears): Aspirin can cause ringing or buzzing in the ears in some people. Reye's syndrome: Children and teenagers with viral infections should not take aspirin, as it can cause a rare but serious condition called Reye's syndrome. Interactions with other drugs: Aspirin can interact with other medications, including blood thinners, anti-inflammatory drugs, and some antidepressants, increasing the risk of side effects. It is important to consult a doctor before taking aspirin, and to always follow the recommended dose and usage instructions.