Muscle relaxants

Muscle relaxants are prescription medicines used after a sudden flare of back or neck pain, especially when muscles feel tight or go into spasm. They are usually prescribed for a few days to a few weeks, not for months.

Common examples are cyclobenzaprine, methocarbamol, metaxalone, carisoprodol and orphenadrine. Cyclobenzaprine is the most studied. Methocarbamol and metaxalone tend to cause less drowsiness, but there is less evidence that they work.

Baclofen and tizanidine (Zanaflex) are approved to treat spasticity, a stiffness caused by conditions such as multiple sclerosis or spinal cord injury. They are sometimes prescribed for back or neck pain too, which is called off-label use.

Despite the name, most of these medicines do not act directly on muscles. They work in the brain and spinal cord, quieting the nerve signals that keep muscles tight. That is also why drowsiness and dizziness are their most common side effects.

Researchers do not fully understand how some of them ease pain. Part of the benefit may come from their calming effect, which can also help people sleep when spasms keep them awake.

They ease symptoms but do not fix the cause of the pain. The hope is to take the edge off while the back or neck settles, so moving and sleeping are easier.

Before you start

Your prescriber will ask about your other medicines, alcohol use, any history of substance use, liver and kidney health, and conditions such as heart rhythm problems, glaucoma or trouble passing urine.

Several common medicines can interact with muscle relaxants, including sleep aids, anxiety medicines, opioid pain medicines, gabapentin and pregabalin, some antidepressants and some antibiotics. Your pharmacist can check your full list.

While you take it

Drowsiness and dizziness are common. Until you know how the medicine affects you, avoid driving, using machinery, or other tasks that need you to be alert.

Guidelines encourage staying as active as you comfortably can during a flare. The medicine is meant to support that, not replace it.

A short record of your pain, sleep and activity can help you and your prescriber judge whether it is worth continuing.

Stopping

Some muscle relaxants, including baclofen, tizanidine and carisoprodol, can cause withdrawal if stopped suddenly after regular use. Your prescriber can explain how to lower the dose slowly.

Most sudden back pain improves a lot over the first several weeks, with or without medicine. For some people, pain lingers or comes back. [20] [21]

For sudden low back pain, American College of Physicians guidelines suggest starting with nondrug care such as heat. If medicine is wanted, they list anti-inflammatory pain relievers (NSAIDs) or muscle relaxants as options. [1]

In a large 2021 review, the common muscle relaxants lowered sudden low back pain by a small amount in the first 2 weeks. That is likely too small for most people to notice, and the quality of the evidence was very low. The same review found no clear improvement in daily function. [2]

In emergency department studies, adding a muscle relaxant to naproxen (Aleve) or ibuprofen (Advil, Motrin) did not improve pain or function a week later, compared with adding a placebo (dummy) pill.

No single muscle relaxant has been shown to work better than the others. There is little research on taking them for more than a few weeks, or for back pain that has lasted for months. [2] [6]

Most studies are of low back pain. There is much less research on muscle relaxants for neck pain.

Common

• Drowsiness and dizziness, which can affect driving, work and caring for others.
• Dry mouth, especially with cyclobenzaprine.
• In studies, side effects were more common with muscle relaxants than with a placebo pill.

Less common

• Cyclobenzaprine is chemically related to older antidepressants called tricyclics. It can cause constipation, blurred vision or trouble passing urine, and it needs extra care in people with glaucoma.
• Cyclobenzaprine is not used by people recovering from a recent heart attack, or who have heart rhythm problems, heart failure or an overactive thyroid.
• Tizanidine can lower blood pressure, causing light-headedness or fainting. It can also affect the liver, so prescribers may check liver blood tests.

Rare but serious

• Combining a muscle relaxant with alcohol, opioid pain medicines, gabapentin or pregabalin, sleep medicines, or benzodiazepines such as alprazolam (Xanax) or diazepam (Valium) can cause extreme sleepiness, slowed breathing and overdose.
• Tizanidine must not be taken with the antidepressant fluvoxamine or the antibiotic ciprofloxacin (Cipro). They can raise tizanidine levels many times over and cause a sharp drop in blood pressure. Many other medicines can raise tizanidine levels or add to its drop in blood pressure. Because the list is long, ask your pharmacist before starting anything new.
• Cyclobenzaprine, and possibly metaxalone, can rarely cause serotonin syndrome when combined with other medicines that raise serotonin, such as many antidepressants and tramadol. Signs include agitation, confusion, sweating, fever, a racing heart and muscle twitching.
• Carisoprodol can lead to misuse and dependence. It has been a federally controlled substance since 2012.
• Stopping baclofen suddenly after regular use can cause withdrawal, starting with confusion, worse stiffness or fever. In severe cases it can bring hallucinations and seizures. Do not stop it on your own.
• Baclofen can build up in people with reduced kidney function and cause confusion or severe drowsiness.

Older adults

Older adults are more likely to have confusion, falls and fractures with these medicines. American Geriatrics Society guidance lists cyclobenzaprine, methocarbamol, metaxalone, carisoprodol, orphenadrine and chlorzoxazone among medicines usually best avoided in people 65 and older.

Baclofen and tizanidine are not on that list, although the same guidance advises avoiding baclofen when kidney function is reduced. One large study also found that older adults taking baclofen or tizanidine had more serious injuries, such as fractures, than those taking cyclobenzaprine.

Other downsides

• When relief comes, it is usually modest and short term.

Get emergency care right away for very slow or shallow breathing, extreme sleepiness or trouble waking, fainting, or high fever with stiff muscles, confusion and a racing heart. Call your prescriber the same day about yellowing of the skin or eyes, or new confusion.