The short answer
- Cyclobenzaprine 5 mg or 10 mg tablets: immediate-release, so splitting is generally acceptable. Ask your pharmacist whether your brand is scored.
- Amrix (extended-release capsules): don’t cut, crush or chew. A lower dose means a different strength, not a split.
- Why split? Usually to take 5 mg instead of 10 mg. Studies found 5 mg three times a day relieves muscle spasm about as well as 10 mg, with less sleepiness.
What is Flexeril (cyclobenzaprine)?
Cyclobenzaprine is a muscle relaxant used for short periods (usually up to 2–3 weeks) to ease painful muscle spasm after strains and sprains, alongside rest, physiotherapy and painkillers. The original brand, Flexeril, has been discontinued in the US, but the name is still widely used for the generic tablets. Cyclobenzaprine is mainly prescribed in the US and Canada; it is not marketed in the UK or Australia, where other approaches are used.
Chemically it’s related to tricyclic antidepressants such as amitriptyline, which explains its side effects: drowsiness, dry mouth, dizziness and constipation, and its interactions.
Can you split the tablets?
| Product |
Strengths |
Split or crush? |
| Cyclobenzaprine HCl tablets (generic, formerly Flexeril; Fexmid 7.5 mg) |
5 mg, 7.5 mg, 10 mg |
Immediate release: splitting generally OK; film coating means it may taste bitter |
| Amrix extended-release capsules |
15 mg, 30 mg |
No – would release the whole day’s dose at once |
The prescribing information for immediate-release tablets doesn’t prohibit splitting, and because the tablets release their dose straight away, a half tablet behaves like a smaller tablet. If your tablet has no score line, halves may be uneven; a pharmacy tablet cutter makes them more consistent, and asking for 5 mg tablets avoids the issue. The general rules are in our guide to taking medicines correctly.
Easier option: ask your prescriber to change the prescription to 5 mg tablets. You get an exact dose, and 5 mg tablets are inexpensive.
How much cyclobenzaprine do you need?
The usual adult dose of immediate-release cyclobenzaprine is 5 mg three times a day, which can be increased to 10 mg three times a day. In trials, 5 mg three times a day gave similar relief to 10 mg with noticeably less drowsiness, which is why many prescribers now start low. Older adults and people with mild liver impairment are usually advised to start at 5 mg and increase slowly, if at all. It shouldn’t be used for more than 2–3 weeks without review.
Cautions and interactions
- Drowsiness: don’t drive until you know how it affects you; avoid alcohol.
- Serotonin syndrome: risk with SSRIs, SNRIs, tramadol, triptans and MAO inhibitors.
- Other sedatives: opioids, benzodiazepines, gabapentin and sleeping tablets add to drowsiness.
- Not suitable after a recent heart attack, with heart rhythm problems, heart failure or an overactive thyroid, or within 14 days of an MAO inhibitor.
- Older adults: higher risk of confusion and falls.
Cyclobenzaprine and surgery
Tell your surgical team you take it. Because it adds to sedation from anaesthetics and opioids, you may be asked to stop it a day or more before surgery; follow their instruction. More on medicines around operations is in the surgery medicines guide.
Frequently asked questions
Can you crush cyclobenzaprine?
Immediate-release tablets can be crushed if swallowing is difficult, but they taste bitter. Never crush or open extended-release Amrix capsules unless the leaflet says you may.
Is half a Flexeril (5 mg) enough?
For many people, yes. Clinical trials found 5 mg three times daily about as effective as 10 mg for acute muscle spasm, with less drowsiness.
How long does cyclobenzaprine take to work?
Usually within an hour, with effects lasting around 4–6 hours for immediate-release tablets.
Can I take cyclobenzaprine with ibuprofen?
Yes, they are often used together for back and neck strains. Take ibuprofen with food and stay within its daily limit.
Sources and further reading
CanforaMedicine Guide
