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What Is a H2 Receptor Antagonist?

By Jacquelyn Gilchrist
Updated Jan 27, 2024
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An H2 receptor antagonist is also known as a histamine H2-receptor antagonist or an H2-blocker. They are a group of medications that may be available over-the-counter or in prescription strength formulas. A doctor may recommend a patient use one of these drugs to treat and prevent certain types of ulcers, as well as to alleviate Zollinger-Ellison disease, which causes the overproduction of stomach acid. When taken in an over-the-counter formula, an H2 receptor antagonist relieves symptoms like acid indigestion, heartburn, and sour stomach. Other possible uses for these types of drugs include treating pancreatic problems, hives, and gastrointestinal damage as a result of trauma or other medicines.

Some examples of H2 receptor antagonists include cimetidine and ranitidine. Famotidine and nizatidine are also classified as H2-blockers. Depending on the specific brand and product the patient uses, these medicines may be available in capsules, chewable or disintegrating tablets, or syrups. Some drugs may also be injected by a health care professional.

The exact daily dosage will vary, depending on which substance the patient is taking, as well as his doctor's instructions. For example, if an adult is using cimetidine to treat ulcers, he will likely be prescribed 300 milligrams (mg) four times daily, while a patient using the same drug to prevent ulcers may take 300 mg only twice daily. Patients must be careful to follow their doctor's exact instructions or to use the directions on the label of over-the-counter products. Some of these drugs may need to be taken with a meal or a full glass of water. Those using over-the-counter H2 receptor antagonists for heartburn should not typically use this product longer than two weeks.

Side effects of an H2 receptor antagonist can vary, depending on which specific drug the patient takes. In general, less severe side effects can include nausea, vomiting, and diarrhea. Stomach pain, constipation, and headaches can also occur. Other side effects may sometimes include drowsiness, dizziness, or cold symptoms, such as sneezing, coughing, or a runny nose. Patients should contact their doctors if these side effects become severe or troublesome.

More serious side effects may require immediate medical attention. Patients should discuss the warning signs with their physicians, which will vary depending on the exact medicine. An H2 receptor antagonist can infrequently cause jaundice, difficulty breathing, or wheezing. Dark urine, fainting, and severe abdominal pain may also occur. Rarely, patients may notice changes in vision, a rapid or irregular heartbeat, or joint pain.

Before using an H2 receptor antagonist, patients should review their other medical conditions, medications, and supplements with either their doctors or pharmacists. As of 2011, the risk of using this type of medication while pregnant is unknown; however, it can pass into breast milk and harm a nursing child. Patients may be unable to use these drugs if they have kidney or liver disease, phenylketonuria, or porphyria. An H2 receptor antagonist may interact with other drugs, including metformin, antacids, and aspirin.

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