7 Cyclobenzaprine Side Effects You Should Know About

If you’ve ever strained a muscle, you know how painful and uncomfortable it can be. Even simple activities and movements can be difficult. To help ease the pain, your healthcare provider may recommend rest and ice, scheduling an Active Release Technique session, or trying rehabilitation exercises.

When needed, certain medications can also provide relief from muscle pain. Over-the-counter (OTC) anti-inflammatory medications and prescription-only muscle relaxants are two common choices. Generally, OTC medications are the first-choice option, and muscle relaxants are used only if further relief is needed. These medications are meant to act as temporary sources of relief as your muscles heal.

Cyclobenzaprine is one of the more common muscle relaxants. It acts in the brain and nervous system to lower pain and tenderness and improve mobility. This oral pill is FDA-approved to relieve muscle spasms that are associated with a short-term muscle injury or pain. So it should only be taken as needed, and for only 2 to 3 weeks at a time.

Although cyclobenzaprine is a low-cost and effective treatment option, it's not necessarily classified as "strong" compared to other muscle relaxants. Cyclobenzaprine can sometimes cause side effects that limit its use. Here are seven of the top cyclobenzaprine side effects to know about.

1. Drowsiness and fatigue

Drowsiness and fatigue are two of the most common side effects of cyclobenzaprine. Taking cyclobenzaprine during the day can cause excessive sleepiness, which can limit your ability to be productive, run errands, and perform daily tasks. 

Cyclobenzaprine comes in three doses: 5 mg, 7.5 mg, and 10 mg. For most people, the standard dose is 5 mg, which is taken 3 times daily as needed. The 10 mg dose is more likely to cause drowsiness than the lower doses.

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If you’re feeling drowsy while taking cyclobenzaprine, talk with your healthcare provider about potentially lowering your dose. Another option is to take the medication at night instead of during the day to lower daytime drowsiness.

Tip: Taking cyclobenzaprine with alcohol or sedative medications like opioids can worsen drowsiness even more. It’s best to avoid these combinations.

2. Dry mouth

Cyclobenzaprine can cause dry mouth, especially in older adults. Dry mouth can make it hard to chew or swallow.

If you have a problem with dry mouth while taking cyclobenzaprine, make sure to hydrate well. The Institute of Medicine of the National Academies recommends aiming to drink 11 to 15 cups of water per day. Keep in mind that caffeinated or sweetened drinks aren’t generally good sources of hydration and don’t count toward these numbers. 

Some other tips to help manage dry mouth include chewing on ice chips and maintaining good oral hygiene. You can also try sugar-free gum or OTC saliva substitutes, which are available as gels, sprays, or lozenges.

3. Headache

Headaches have been reported as a common side effect of cyclobenzaprine. Headaches may not need medical attention, but it’s important to note that they could happen.

Headaches tend to go away as your body adjusts to the medication. But you can also take an OTC pain medication, such as acetaminophen (Tylenol), with your healthcare provider’s OK.

4. Upset stomach

Cyclobenzaprine can cause an upset stomach or nausea. This is not as common as some of the other listed side effects. Still, to prevent gut-related issues, it’s a good idea to take cyclobenzaprine with food.

If you do experience this side effect, it’s a good idea to avoid spicy, fried, and high-fiber foods. Sticking to bland foods, such as toast or bananas, can also help. Taking an OTC medication — such as Pepto-Bismol (bismuth subsalicylate), Mylanta (aluminum hydroxide/magnesium hydroxide/simethicone), or Tums (calcium carbonate) — is another way to soothe an upset stomach.

5. Trouble focusing

As mentioned above, cyclobenzaprine can make you drowsy. This can make it harder to focus and be alert. When you first start taking cyclobenzaprine, you may need to avoid certain tasks that require alertness until you learn how the medication affects you. It’s especially important to avoid driving and operating other kinds of heavy machinery while you’re adjusting to cyclobenzaprine. 

Certain people are more likely to experience focus changes than others. This side effect can be more severe if you take cyclobenzaprine with alcohol or other medications that also cause drowsiness. Older adults and people taking doses above 5 mg might have trouble focusing every time they take cyclobenzaprine. 

6. Heart rhythm changes

Heart rhythm changes are a rare but serious cyclobenzaprine side effect. These cardiac-related issues have been reported to occur in less than 1% of people taking the 10 mg dose in clinical trials.

Older adults may be more at risk for heart rhythm changes. People ages 65 years and older generally shouldn’t start cyclobenzaprine at a dose higher than 5 mg. And it’s not recommended to be used at all in people with certain pre-existing heart conditions.

If you feel or detect an irregular heartbeat, become very lightheaded, or suddenly become short of breath while taking cyclobenzaprine, visit the emergency room (ER) right away. You may need additional tests to see if your heart rhythm has been affected.

7. Serotonin syndrome

Serotonin syndrome — when there is too much of the chemical serotonin in the brain — is another rare but serious side effect linked to cyclobenzaprine. It doesn’t usually develop from cyclobenzaprine alone; the drug itself has a small effect on serotonin. But taking cyclobenzaprine with other medications that affect serotonin can raise the risk of serotonin syndrome. This includes medications like selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), triptans, and more.

Symptoms of mild serotonin syndrome can include a fast heart rate, sweating, and trouble sleeping. More severe symptoms can include confusion, fever, and even agitation. If you feel these symptoms, it’s important to alert your healthcare provider right away and ask about next steps.

When should I contact my healthcare provider about cyclobenzaprine side effects?

Most mild cyclobenzaprine side effects resolve as your body adjusts to the medication. But if side effects persist or worsen, make sure to speak with your healthcare provider. They may adjust your cyclobenzaprine dosage or recommend taking another medication altogether.

In certain situations, it’s important to seek medical care right away. Visit the nearest ER if you have any of these serious symptoms after taking cyclobenzaprine:

• Seizures 

• Irregular heart beat

• Severe drowsiness

• Hallucinations

Keep in mind: Feeling any of these side effects could mean there is too much cyclobenzaprine in the body. Proactive emergency care can help make sure these symptoms do not turn into something more serious. 

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Written by:

Hindu Rao, PharmD, APh, BCACP

Hindu Rao, PharmD, APh, BCACP is a clinical assistant professor of pharmacy practice at Chapman University School of Pharmacy and a clinical pharmacist at Providence Medical Foundation. She specializes in chronic disease management and has her board certification in ambulatory care.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

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