Muscle relaxers are often prescribed to help with muscle spasms, pain related to muscle tension, and mobility issues with conditions like fibromyalgia, back pain, multiple sclerosis, or strains and sprains. They may be prescribed for short-term relief or as part of a long-term pain management plan.

If you’re prescribed muscle relaxers, it’s important to know how they work in the body, what factors can influence their effectiveness, and what you can expect in terms of side effects.

What Are Muscle Relaxers?

Muscle relaxers, also known as muscle relaxants, are a class of medications used to treat muscle spasms or spasticity. They relax the muscles and ease pain in one of two ways:

• Centrally acting muscle relaxants act on the central nervous system to decrease muscle tone, or the state of contraction of the muscle.[1] Common centrally acting muscle relaxants include Flexeril (cyclobenzaprine), Robaxin (methocarbamol), Soma (carisoprodol), and baclofen.
• Direct-acting muscle relaxants work directly on the muscle tissue, such as dantrolene.[2] It’s used to treat spasticity in conditions like spinal cord injuries, multiple sclerosis, and cerebral palsy.

Some medications are not muscle relaxers but may be prescribed for their sedative and muscle-relaxing properties, such as benzodiazepines like diazepam or lorazepam.

How Long Do Muscle Relaxers Last?

Muscle relaxers have different durations based on several factors, including the specific medication, dosage, route of administration, and individual metabolism.

Cyclobenzaprine

Cyclobenzaprine takes effect approximately one hour after administration and reaches its peak effectiveness in 4 to 8 hours.[3] The effects last 12 to 24 hours. Cyclobenzaprine’s half-life is about 18 hours, but it can range from 8 to 37 hours.[4] This means that it’s mostly eliminated from the body within 90 hours, but the range can be from 40 hours to 185 hours. Extended-release cyclobenzaprine has a half-life of approximately 32 hours and is eliminated from the body for about 160 hours.[5]

Methocarbamol

Methocarbamol takes effect approximately 30 minutes after administration and reaches its peak effectiveness in 1 to 2 hours.[6] The effects last 4 to 6 hours. Methocarbamol’s half-life is about 1 to 2 hours, so it lasts 5 to 10 hours in the body.[7]

Carisoprodol

Carisoprodol takes effect approximately 30 minutes after administration and reaches its peak effectiveness in 1 to 2 hours.[8] The effects last 4 to 6 hours. Carisoprodol has a half-life of approximately 2 hours, meaning it remains in your system for about 10 hours.[9]

Tizanidine

Tizanidine takes effect approximately one to two hours after administration and reaches its peak effectiveness in two hours.[10] The effects last 4 to 6 hours. Tizanidine’s half-life is approximately 2.5 hours, meaning it remains in your system for 10 to 12 hours.[11]

Baclofen

Baclofen takes effect approximately one hour after administration and reaches its peak effectiveness within 2 to 3 hours.[12] The effects last 4 to 8 hours. Baclofen’s half-life is 2 to 6 hours, so it stays in the body for 10 to 30 hours.[13]

Factors That Affect Duration

Several factors can influence how long a muscle relaxer lasts in your system:[14,15]

• Metabolism: Individuals with faster metabolic rates may process and eliminate muscle relaxants more quickly.
• Age: Older adults typically metabolize medications more slowly, resulting in a longer duration of action.
• Organ function: Most muscle relaxers are metabolized by the liver and excreted through the kidneys. Impaired liver and kidney function can cause the drug to remain in the body for a longer period.
• Dosage and frequency: Higher doses or repeated doses may accumulate in your system, especially with the drugs that have longer half-lives.
• Drug interactions: Some muscle relaxers interact with other medications, including opioids, antidepressants, and alcohol, leading to more intense effects or longer duration.
• Formulation: Some muscle relaxers are available in different formulations, such as extended-release cyclobenzaprine, which may last longer than the immediate-release version.

What to Expect When Taking Muscle Relaxers

Muscle relaxers can provide relief from pain, muscle tension, and spasticity, especially when combined with a comprehensive pain management plan that includes rest, physical therapy, and heat therapy. However, they do have side effects and safety considerations.

Many muscle relaxers begin to take effect within 30 minutes to an hour. Pain relief typically peaks around 1 to 3 hours after the last dose and lasts from 4 to 24 hours, depending on the specific medication.

Muscle relaxers have the side effect of drowsiness or sedation, particularly cyclobenzaprine and carisoprodol. Dizziness, dry mouth, fatigue, blurred vision, and nausea or upset stomach are also common.

Muscle relaxers can be habit-forming. They’re usually prescribed short-term to avoid tolerance and dependence, but they may be used in the long term as part of a comprehensive pain management plan.

If you’re taking a muscle relaxer, it’s important to avoid mixing your prescription with any drugs that can increase the sedative effects, such as central nervous system (CNS) depressants like benzodiazepines, sleep aids, opioids, or alcohol. Doing so can amplify the drowsiness and increase the risk of dangerous effects like respiratory depression or severe impairment. It’s essential to avoid driving or engaging in other tasks that require focus and attention after taking muscle relaxants.

Are Muscle Relaxers Addictive?

Yes, some muscle relaxers are controlled substances because of their potential for misuse, abuse, and addiction. Dependence can develop even if you take the drug as prescribed, but the risk is much higher with misuse or abuse. If you stop taking it suddenly or reduce your dose, you could experience withdrawal symptoms like anxiety, insomnia, or tremors.

Some muscle relaxers have a higher risk of misuse, however. Carisoprodol is a Schedule IV controlled substance because of its abuse potential.[16] It’s metabolized into meprobamate, a drug with known sedative and dependence effects. Cyclobenzaprine is not a controlled substance, but in rare cases, high doses may lead to central nervous system effects such as drowsiness, dizziness, or confusion; however, it is not commonly associated with euphoria or significant misuse potential.[17]

Suppose you find yourself taking larger doses than prescribed, using the drug for its sedative or calming effects instead of for muscle pain relief, or requiring more frequent dosing to get the same effects. In that case, you may be developing an addiction to your muscle relaxers. Addiction is more than physical dependence and withdrawal – it requires comprehensive treatment for the compulsive need to use the drug despite consequences.

Muscle relaxers can provide effective relief for muscle pain, spasms, and discomfort. Each drug has different onset, duration, and elimination times, however. Some muscle relaxers wear off in just a few hours, while others stay in your system for a day or longer. It’s important to understand how your medication works and how long it lasts to ensure you use it responsibly.