What are the Common Cimetidine Side Effects?

Common side effects that can arise from treatment with cimetidine range from mild to severe. Mild cimetidine side effects include drowsiness, headache, dizziness, and diarrhea. More severe cimetidine side effects include anxiety, hallucinations, muscle pain, breast enlargement, and allergic reactions like difficulty breathing, hives, or swelling in the face.

Cimetidine is used to treat gastroesophageal reflux disease (GERD) and ulcers in the stomach. It works by blocking the action of histamine, a chemical that contributes to the release of acid into the stomach. Cimetidine is available both over the counter and by prescription. It should not be taken for a period longer than two weeks. If symptoms persist, a medical professional should be consulted.

Mild cimetidine side effects such as drowsiness, headache, dizziness, and diarrhea should go away quickly. If they persist, or if they increase in severity, a patient should contact his or her doctor. Any patient who experiences severe side effects such as hallucinations or abrupt changes in mood like hyperactivity, confusion, nervousness, or depression should stop taking the medication and see his or her doctor immediately.

Treatment with cimetidine can enhance the activity of estrogen in the body. Cimetidine side effects which come as a result of enhanced estrogen can result in lower metabolism, breast enlargement in males — called gynecomastia — and the flow of milk from a woman's breasts when she is not nursing — called galactorrhea. Cimetidine has also been shown to affect methadone metabolism.

One of the most common cimetidine side effects is drowsiness. Patients beginning a treatment regimen with cimetidine should exercise caution when driving or working with heavy machinery. One should not drink alcohol while being treated with cimetidine.

Pregnant women should talk to their doctors before taking cimetidine. Mothers who are breast-feeding should not take cimetidine because the medication has been found in breast milk. Adults who are 65 or older are more susceptible to cimetidine side effects than are younger adults, so they should talk to their doctors about safer treatment options. Treating children with cimetidine should be approached with great caution. Studies have not established the safety or efficacy of cimetidine for children younger than 16.

Cimetidine is known to interact with numerous other medications. Patients who take medicine for psychiatric conditions, heart disease, high blood pressure, or cancer are at risk for severe and potentially life-threatening cimetidine side effects. Anybody contemplating a treatment regimen with cimetidine should talk to a medical professional and disclose all medications, supplements, herbal products, or vitamins he or she is taking.