Flexeril (cyclobenzaprine) is taken as a tablet by mouth, typically three times a day, for no longer than two to three weeks. The standard starting dose is 5 mg three times daily, which can be increased to 10 mg three times daily based on how you respond. You can take it with or without food.
Standard Dosing Schedule
Most prescriptions start at 5 mg taken three times a day, spacing doses roughly evenly throughout the day. If that dose isn’t providing enough relief, your prescriber may bump it up to 10 mg three times a day, for a maximum of 30 mg per day. The immediate-release tablet can be taken with or without food, and should be swallowed whole.
There is also an extended-release capsule form (sold as Amrix) that’s taken once daily. If you have this version, swallow the capsule whole. Do not crush, chew, or open it, since the coating controls how the medication releases into your body over time.
Why It’s Only Prescribed Short-Term
Flexeril is approved for a maximum of two to three weeks of continuous use. That limit exists for two reasons: there isn’t strong evidence that it works beyond that window, and the type of muscle spasm it treats (acute, injury-related tightness) typically resolves on its own within that timeframe. If your pain hasn’t improved after two or three weeks, the underlying issue likely needs a different approach rather than more of the same medication.
How Flexeril Works
Flexeril doesn’t act directly on your muscles. Instead, it works inside the brain and spinal cord, dialing down the nerve signals that cause muscles to spasm. Specifically, it reduces the activity of motor neurons that control muscle reflexes. It also blocks certain serotonin pathways in the spinal cord that transmit pain signals. The result is less involuntary tightness and less pain, without actually weakening the muscle itself.
Because it acts on the central nervous system, Flexeril causes significant drowsiness in many people. This is worth knowing before your first dose.
Common Side Effects
Drowsiness is the most frequently reported side effect and often the most noticeable. Dry mouth and dizziness are also common. These effects tend to be strongest in the first few days as your body adjusts. Taking your dose closer to bedtime (if your schedule allows for three-times-daily dosing) can help you work around the drowsiness during the day, though you’ll likely still feel some sedation with daytime doses.
Because of how sedating it can be, avoid driving or operating heavy machinery until you know how the medication affects you personally. Some people tolerate it well; others feel significantly impaired.
Alcohol and Other Sedating Substances
Alcohol amplifies the drowsiness, dizziness, and impaired concentration that Flexeril already causes on its own. Combining the two can make it difficult to think clearly and significantly slow your reaction time. The same applies to other sedating substances like sleep aids, antihistamines, and opioid pain medications. If you’re taking any of these alongside Flexeril, the sedative effects stack on top of each other.
Drug Interactions to Know About
The most dangerous interaction involves a class of antidepressants called MAO inhibitors. Combining Flexeril with an MAO inhibitor, or taking Flexeril within 14 days of stopping one, can trigger a life-threatening reaction involving dangerously high body temperature and seizures. This isn’t a theoretical risk; deaths have been reported.
Flexeril also carries a risk when combined with medications that raise serotonin levels, including many common antidepressants (SSRIs and SNRIs). Because Flexeril itself blocks serotonin pathways, stacking it with other serotonin-active drugs can push levels too high, a condition called serotonin syndrome. Symptoms include agitation, rapid heartbeat, high body temperature, and muscle twitching. If you take any antidepressant, make sure your prescriber knows before you start Flexeril.
Who Should Not Take Flexeril
Flexeril is not safe for people with certain heart conditions, including heart failure, recent heart attack, irregular heart rhythms, or heart block. It’s also contraindicated if you have an overactive thyroid. People with moderate to severe liver disease should not take it either, since the liver is responsible for breaking the drug down; impaired liver function means the medication lingers in your system much longer than intended, intensifying side effects.
Older adults are more sensitive to Flexeril’s sedating effects and the associated fall risk. Prescribers often use lower doses or avoid the drug entirely in this group.
What to Do if You Miss a Dose
If you miss a dose, take it as soon as you remember. If it’s already close to the time for your next scheduled dose, skip the missed one and continue with your regular schedule. Don’t double up to make up for a missed dose, since doing so increases the risk of excessive drowsiness and other side effects.