Cyclobenzaprine

Key facts

• Cyclobenzaprine is a centrally acting muscle relaxant, chemically related to tricyclic antidepressants. It eases muscle spasm from acute injuries such as back or neck strain, working in the brain and spinal cord rather than on the muscle itself.
• It's usually taken for short courses of two to three weeks alongside rest and physical therapy; longer use has not been shown to add benefit.
• Never combine cyclobenzaprine with an MAOI (monoamine oxidase inhibitor), or take it within 14 days of stopping one. Together they can cause a severe, sometimes fatal reaction with high fever, seizures, and wild swings in blood pressure.
• Seek urgent care for a fast or irregular heartbeat, severe confusion or hallucinations, or fainting.

What cyclobenzaprine treats

Cyclobenzaprine treats muscle spasm associated with acute, painful musculoskeletal conditions such as back strain, neck strain, and other soft-tissue injuries. It is meant for short-term relief while you rest and begin rehabilitation, not for ongoing muscle spasticity caused by conditions like cerebral palsy or spinal cord disease, which need different medicines.

How cyclobenzaprine works

Cyclobenzaprine acts in the brainstem, reducing the nerve signals that keep muscles tight after an injury; it does not act directly on the muscle fibres. Because its structure closely resembles tricyclic antidepressants, it also carries similar anticholinergic and sedating effects, such as dry mouth and drowsiness.

Before you take it

• Do not take cyclobenzaprine with an MAOI, or within 14 days of stopping one.
• Avoid it if you have had a recent heart attack, heart failure, an irregular heart rhythm, or an overactive thyroid; the drug's effect on heart rate can worsen these conditions.
• Tell your prescriber about other sedating medicines, antihistamines, antidepressants, or opioids you take. Combined with cyclobenzaprine, they deepen drowsiness and slow breathing.
• Use caution if you are pregnant or breastfeeding, since safety data are limited.

Side effects

Drowsiness and dry mouth are common, especially when you start treatment. Dizziness on standing, blurred vision, and constipation can also occur.

Stop and seek urgent medical care for:

• A fast or irregular heartbeat.
• Severe confusion, agitation, or hallucinations.
• Swelling of the face, lips, or throat, or difficulty breathing.
• Fainting or persistent light-headedness.

Safety essentials

• The MAOI rule is absolute. Combining cyclobenzaprine with an MAOI, or starting one too soon after stopping cyclobenzaprine, can cause a fatal reaction; always tell every prescriber about both medicines.
• Alcohol and other sedating drugs multiply the drowsiness cyclobenzaprine causes; avoid driving or operating machinery until you know how it affects you.
• Older adults are more sensitive to its sedating and anticholinergic effects and have a higher risk of falls and confusion; a lower dose or a different medicine is often safer.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.