H2 blockers – also known as histamine 2 receptor antagonists – are medications used to treat various gastrointestinal disorders. These drugs work by decreasing the amount of acid produced by the stomach. They tend to provide longer-lasting relief from symptoms than some other types of medications, such as antacids. 

Many conditions involving excess stomach acid may be treated with H2 blockers. These include peptic ulcers, gastroesophageal reflux disease (GERD) and esophagitis. H2 blockers may also be used for milder conditions such as heartburn and indigestion. They are available both with and without a prescription, depending on their strength, and may be administered as an oral solution, tablet or injection.

H2 blockers take time to begin working. Usually, several days pass before the patient notices relief from symptoms. In rare cases, some patients who take these drugs will experience side effects such as mild diarrhea, dizziness and fatigue. Symptoms of overdose can be similar to the medication’s side effects but are usually more severe.

Patients who have certain medical conditions – such as liver or kidney damage, or phenylketonuria (PKU) – should use H2 blockers with caution. Several types of drugs also interact poorly with H2 blockers. Patients who smoke may find that this habit negates the beneficial effects of H2 blockers. Cigarette smoke increases the production of acid in the stomach, particularly overnight.