GERD Home > Cimetidine Side Effects

Common side effects of cimetidine include such things as headaches, diarrhea, dizziness, and drowsiness. If problems do occur, they tend to be mild and easily treated; however, there are some side effects that you should report to your healthcare provider immediately, such signs of an allergic reaction (swelling of the mouth or throat, or difficulty breathing).

An Introduction to Cimetidine Side Effects

As with any medicine, side effects are possible with cimetidine (Tagamet®); however, not everyone who takes this drug will experience problems. In fact, most people tolerate it well. If side effects do occur, in most cases, they are minor, meaning they require no treatment or are easily treated by you or your healthcare provider.
(This article covers many, but not all, of the possible side effects with cimetidine. Your healthcare provider can discuss a more complete list of cimetidine side effects with you.)

Common Side Effects of Cimetidine

Cimetidine has been studied thoroughly in clinical trials, in which a group of people taking the drug have side effects documented and compared to another group not taking the medicine. This way, it is possible to see what side effects occur, how often they appear, and how they compare to the group not taking the medicine.
In these studies, the most common cimetidine side effects included:
  • Breast enlargement in men (gynecomastia) -- in up to 4 percent of people (see Cimetidine and Gynecomastia)
  • Headaches -- up to 3.5 percent
  • Diarrhea -- up to 1 percent
  • Dizziness -- up to 1 percent
  • Drowsiness -- up to 1 percent.
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Last reviewed by: Kristi Monson, PharmD;
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