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Indigestion or heartburn, dry mouth, and dizziness are the most common side effects reported with Amrix. Side effects that are rare but possible (occurring in less than 1 percent of people taking the drug) include insomnia, diarrhea, and double vision. While most side effects of Amrix are minor, some require immediate medical attention, such as difficulty urinating, fainting, or feelings of a rapidly beating heart.
As with any medicine, side effects are possible with Amrix® (cyclobenzaprine ER). However, not everyone who takes the medication will have problems. In fact, most people tolerate it quite well. If side effects do occur, in most cases, they are minor and either require no treatment or can easily be treated by you or your healthcare provider.
(This article covers many, but not all, of the possible side effects with Amrix. Your healthcare provider can discuss a more complete list of Amrix side effects with you.)
Amrix has been studied thoroughly in clinical trials. In these studies, the side effects that occur in a group of people taking the drug are documented and are then compared to side effects that occur in another group of people 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 Amrix side effects included:
- Dry mouth -- in up to 14 percent of people (see Amrix and Dry Mouth)
- Dizziness -- up to 6 percent
- Indigestion or heartburn -- up to 4 percent
- Nausea -- up to 3 percent
- Fatigue -- up to 3 percent
- Constipation -- up to 3 percent
- Drowsiness -- up to 2 percent.
In general, studies suggest that taking Amrix (an extended-release version of cyclobenzaprine) once daily causes less daytime drowsiness compared to taking regular, short-acting cyclobenzaprine three times daily.