The most commonly prescribed muscle relaxers in the United States include cyclobenzaprine (Flexeril), methocarbamol (Robaxin), tizanidine (Zanaflex), baclofen (Lioresal), and metaxalone (Skelaxin). These medications fall into two broad categories depending on whether they treat sudden muscle spasms or ongoing muscle tightness from neurological conditions, and the distinction matters because it determines which drug a provider will choose.
Two Types of Muscle Relaxers
Muscle relaxers split into two functional groups: antispasmodics and antispastics. Antispasmodics treat the acute muscle spasms that come with injuries, strains, and back pain. These are the ones most people picture when they think of muscle relaxers. The antispasmodic group includes cyclobenzaprine, methocarbamol, metaxalone, carisoprodol (Soma), chlorzoxazone, and orphenadrine (Norflex).
Antispastics work differently. They target the constant muscle tightness, or spasticity, that occurs in conditions like multiple sclerosis, cerebral palsy, and spinal cord injuries. Baclofen and dantrolene (Dantrium) are the main antispastic options. Two drugs, tizanidine and diazepam (Valium), can function as both antispasmodic and antispastic, making them versatile choices for different situations.
How They Work in the Body
Despite being grouped together, these medications don’t all do the same thing at a cellular level. Antispasmodic drugs like cyclobenzaprine, methocarbamol, and orphenadrine act primarily on the brain stem, dialing down hyperactive muscle reflexes before the signal ever reaches your muscles. They don’t relax the muscle directly. Instead, they quiet the overactive nerve signaling that causes the muscle to seize up.
Antispastic drugs take a different route. Baclofen and diazepam mimic a calming brain chemical called GABA, which dampens nerve activity in the spinal cord and reduces muscle tone. Dantrolene is unique in that it works directly on the muscle fiber itself rather than the nervous system, blocking the release of calcium that muscles need to contract.
The Most Frequently Prescribed Options
Cyclobenzaprine is by far the most widely prescribed muscle relaxer in the U.S. It’s typically used for neck pain, back strains, and musculoskeletal injuries. It’s structurally similar to older antidepressants, which explains why drowsiness is its most prominent side effect. In clinical studies, somnolence was the most common complaint, and the rate of drowsiness climbed nearly 20% when patients moved from low to high doses.
Methocarbamol is another popular choice, often preferred because it tends to cause less sedation than cyclobenzaprine. It’s available in both oral and injectable forms and is commonly used for acute back pain and muscle injuries.
Tizanidine occupies a middle ground. It works for both spasm and spasticity, and its shorter duration of action means the sedation wears off faster. This makes it a reasonable option when people need relief but also need to function during the day.
Baclofen is the go-to for spasticity from neurological conditions. It can be taken orally or, in severe cases, delivered directly into the spinal fluid through an implanted pump. People with reduced kidney function need to be especially cautious with baclofen, as impaired clearance of the drug can lead to confusion and altered mental status requiring hospitalization.
Metaxalone (Skelaxin) rounds out the common prescriptions. It causes slightly less drowsiness than cyclobenzaprine and is generally well tolerated, though it can occasionally affect liver enzymes.
Common Side Effects
Drowsiness is the universal side effect across nearly all muscle relaxers. Beyond that, expect dizziness, dry mouth, and fatigue. These drugs work on the central nervous system, so anything that involves alertness, coordination, and reaction time can be affected. Driving or operating heavy equipment while taking them is risky.
Cyclobenzaprine, orphenadrine, and some others also carry anticholinergic effects, meaning they can cause dry mouth, blurred vision, constipation, and difficulty urinating. These effects are especially problematic for older adults.
Combining a muscle relaxer with alcohol, opioids, or sedatives amplifies the sedation dramatically and can suppress breathing. Using three or more drugs that act on the central nervous system at the same time significantly increases the risk of falls and fractures.
Duration of Use and Dependency Risk
Muscle relaxers for acute pain are meant to be short-term medications. Clinical guidelines recommend limiting antispasmodic use to about two weeks for conditions like acute low back pain. Beyond that window, the evidence for benefit drops off, and the risk of dependency and side effects rises. Physical therapy, stretching, and other non-drug approaches are typically encouraged alongside or instead of continued medication use.
Carisoprodol (Soma) stands apart from the rest because it carries a real dependency risk. The DEA classifies it as a Schedule IV controlled substance, the same category as benzodiazepines like diazepam and alprazolam. Carisoprodol is metabolized into a compound that produces effects similar to barbiturates, which is why it has a history of misuse. Many providers avoid prescribing it altogether when safer alternatives exist. Diazepam is also Schedule IV and carries its own well-documented potential for dependence.
Risks for Older Adults
The American Geriatrics Society explicitly recommends avoiding most muscle relaxers in people over 65. Their Beers Criteria, a widely used safety guide for prescribing in older adults, lists carisoprodol, chlorzoxazone, cyclobenzaprine, metaxalone, methocarbamol, and orphenadrine as medications to avoid. The reasoning is straightforward: older adults are more sensitive to the sedation and anticholinergic effects, the drugs are poorly tolerated at doses that actually work, and the resulting drowsiness and unsteadiness significantly increase the risk of falls and fractures. The quality of evidence behind this recommendation is moderate, and the strength of the recommendation is strong.
For baclofen specifically, older adults with impaired kidney function face added danger. If baclofen can’t be avoided, guidelines recommend the lowest possible dose with close monitoring for confusion or changes in mental status.
Over-the-Counter Alternatives
No true muscle relaxers are available without a prescription in the U.S., but several over-the-counter options can help with muscle pain and tension. Ibuprofen and naproxen reduce inflammation that contributes to muscle tightness, while acetaminophen addresses pain directly.
Magnesium supplements are a popular natural option. Magnesium plays a role in muscle contraction and relaxation, and people who are deficient may experience more cramping. High doses can cause stomach cramps and diarrhea, so starting with a modest amount makes sense.
Topical options include capsaicin cream, which works by depleting the chemical that transmits pain signals from nerve endings, and menthol or peppermint oil, which creates a cooling sensation that can override pain signals. Arnica gel is another topical option used for soreness, though it should never be ingested because high doses taken by mouth can be dangerous. CBD oil has gained popularity for muscle relief, but its legal status varies by state and it can interact with other medications.