Downsides

If you are between the ages of 18 and 60, do not take any other medications, and have no other medical conditions, you are more likely to experience the following side effects:

• Sedation. This is a serious side effect that can impair reaction time and make it difficult to drive or operate machinery. Stay away from alcohol.
• Dry mouth, fatigue, difficulty urinating, an increase in eye pressure, headache, dizziness, blurred vision, or nausea are also common side effects.
• Should only be used on a temporary basis (for periods of up to two to three weeks only)
• Muscle spasms caused by cerebral or spinal cord disease, or in children with cerebral palsy, are ineffective.
• Cyclobenzaprine should never be given within 14 days of antidepressants that inhibit monoamine oxidase (MAO), as the combination can be fatal.
• Serotonin syndrome may result from interactions with other medications that also boost serotonin (such as antidepressants, tramadol, St. John's Wort, and bupropion). The signs and symptoms include altered mental status (such as agitation, hallucinations, coma, and delirium), rapid heartbeat, flushing, numbness or rigidity in the muscles, and stomach discomfort (including nausea, vomiting, and diarrhea)
• Alcohol, other CNS depressants, and tricyclic antidepressants (such as amitriptyline and imipramine) may all have stronger effects or negative effects when used with cyclobenzaprine.
• People with arrhythmias, heart block or conduction issues, heart failure, hyperthyroidism, or those who have recently had a heart attack would not be a good candidate.
• In patients with mild liver illness, the recommended dosage of cyclobenzaprine should be decreased. People with mild to severe liver problems shouldn't take it.
• Cyclobenzaprine may not be appropriate for people with glaucoma or high intraocular pressure, a history of urinary retention, or who are taking other medications with anticholinergic side effects (anticholinergic side effects include constipation, blurred vision, and increase in eye pressure).
• Muscle spasms caused by brain injury or disease are ineffective.
• Seniors may be more sensitive to the effects of cyclobenzaprine, so the dosage should be kept low if the benefits outweigh the risks.

Seniors and children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures), or people who take other medications are more likely to experience a broader range of side effects.