Muscle relaxers are medications that are commonly prescribed to treat a wide range of muscle-related symptoms, which include everything from spasms to spasticity. While all muscle relaxers provide similar advantages, they can work differently. Whether you are about to start a new job or want to make sure about contraindications, you should know how long these medications remain in your body.
Understanding Muscle Relaxers
Muscle relaxers are a category of prescription medications designed specifically to alter muscle function. Doctors may recommend these medicines when rest, stretching, or over-the-counter pain relievers are not enough to manage muscle pain or stiffness. Muscle relaxers can be separated into two distinct types: antispasmodics and antispasticity agents.
Antispasmodics are typically used to treat muscle spasms and conditions that cause these symptoms. It’s common for muscle spasms to develop when a tendon, ligament, or muscle is injured. If you experience a strain or sprain in your lower back, muscle spasms might occur.
Antispastics are administered for the treatment of muscle spasticity, which is a symptom that involves tightness in the muscles. Keep in mind that there are no over-the-counter muscle relaxers in the US. These medications need to be prescribed by a healthcare professional.
A few of the more commonly prescribed antispastics include:
- Dantrolene
- Baclofen
- Tizanidine
- Diazepam
Note: diazepam and tizanidine can be prescribed for antispastic and antispasmodic applications.
The most commonly prescribed antispasmodics include:
- Carisoprodol
- Chlorsoxazone
- Cyclobenzaprine
- Metaxalone
- Methocarbamol
- Orphenadrine
How Muscle Relaxers Work in the Body
Skeletal muscles know when to relax or contract based on messages that are sent from your brain and through your central nervous system. If a muscle spasm occurs when you don’t want it to, you can take muscle relaxers that should calm it down. When you consume this type of medication, it will depress or sedate your central nervous system to effectively interrupt the signal between your brain and muscles.
Each muscle relaxer is absorbed, metabolized, and excreted at a different time, which means that the half-life of the medication varies.
Half-Life of Common Muscle Relaxers
Regardless of the symptom or condition you are treating, it helps to know how long a muscle relaxer stays in your system. A drug’s half-life is the time it takes for the amount of medicine in your blood to drop by half. Most medicines are mostly cleared after about five half-lives.
Below are approximate half-lives for some commonly prescribed skeletal muscle relaxers:
- Cyclobenzaprine (Flexeril): About 8 to 37 hours, with an average of around 18 hours.
- Carisoprodol (Soma): Around 2 to 2.5 hours. Its active metabolite, meprobamate, has a longer half-life of about 6 to 17 hours, so it can stay in the body longer, especially with regular use.
- Baclofen: Usually 2 to 6 hours after an oral dose.
- Tizanidine: Roughly 2 to 4 hours.
Because of its longer half-life, cyclobenzaprine can remain in your body for several days. In many people, it’s mostly cleared within about 3 to 8 days after the last dose, depending on factors like age, liver function, and dose.
These ranges are averages, not exact predictions. Your own clearance time can be longer if you are older, have liver or kidney problems, or take other medicines that affect how your body processes drugs. Always ask your prescriber or pharmacist how long your specific medication is likely to stay in your system.
Factors Affecting Duration in the Body
Many factors determine how long muscle relaxers remain in your system. These include everything from liver and kidney function to your dosage and the frequency of use. Your kidneys and liver help to break down any medications you take. If you suffer from liver failure or a similar condition, the rate of metabolism reduces, which can lead to the drug remaining in your body for longer.
In this scenario, a higher amount of the drug can reach your circulation, which can be dangerous depending on the dose. These factors can be highly varied among different people. Muscle relaxers will also stay in your system longer if you have poor health or a larger body mass.
Muscle Relaxers and Drug Testing
If you’re getting ready to start a job, you may be wondering how long muscle relaxers show up on a drug test. Even though these medications usually aren’t detectable during a routine drug test, you may still want to avoid taking them just to be careful. Below are the timeframes during which different types of muscle relaxers can be detected:
| Drug | Blood Test Detection Window | Urine Sample Detection Window | Saliva Sample Detection Window |
| Baclofen | 72 hours | 48 hours | 48–72 hours |
| Soma | 24 hours | Two to three days | Up to 4 hours |
| Flexeril | Up to 10 days | Up to four days | Three to nine days |
Safety Considerations and Potential Risks
Even if you’re given a small dose of a muscle relaxer, there are some safety considerations and possible risks that you should keep in mind. While these medications have proven effective at treating a wide range of symptoms, taking high doses can result in harmful side effects. However, each type of muscle relaxer has its own unique side effects.
The most common side effects associated with muscle relaxers include:
- Headaches
- Drowsiness and fatigue
- Dizziness
- Dry mouth
- Nausea
If you experience any of these side effects, please consult your doctor immediately. When you receive a prescription for a muscle relaxer, you may want to take it under medical supervision the first time to ensure you’re following the instructions properly.
Can You Become Addicted to Muscle Relaxers?
Muscle relaxers can be very helpful for muscle spasms, injuries, back pain, and conditions such as ALS, MS, or cerebral palsy. Many common options, including diazepam (Valium), carisoprodol (Soma), cyclobenzaprine, and tizanidine, act on the central nervous system, and some are controlled substances.
Because they slow brain and spinal cord activity, muscle relaxers can be habit-forming, even when you start using them as prescribed. This can lead to:
- Physical dependence, when your body has adapted to the drug, and you may have withdrawal symptoms if you stop suddenly.
- Addiction, when you feel compelled to keep taking the drug for its calming or “high” effects, even when it causes problems.
Signs that you or someone close to you may be misusing muscle relaxers include:
- Continuing to use them after pain or spasms have improved
- Needing higher doses to feel the same effects
- Wanting to stop but being unable to do so
- Faking or exaggerating symptoms to get more pills
- Focusing on the medication, neglecting work, hobbies, or self-care
- Sudden changes in mood or sleep, or ongoing drowsiness and low blood pressure
Risk is higher if you have chronic pain, a history of substance use, mental health conditions such as PTSD, or a family history of addiction. Avoid drinking alcohol or using other sedating drugs while taking a muscle relaxer because the combination can lead to extreme drowsiness, breathing problems, overdose, coma, or death.
Managing Muscle Relaxer Use
To use muscle relaxers safely, keep the following guidelines in mind:
- Do not take more of your muscle relaxer or use it more often than prescribed. This will put you at a higher risk of becoming dependent on the substance.
- When you experience side effects or notice that symptoms aren’t improving, you should speak with your doctor.
- If you believe you are becoming dependent on muscle relaxers, talk with your provider about addiction treatment options or a referral to a specialist.
- If your symptoms mirror those of an overdose, call 911 immediately.
If you’re looking to manage muscle pain or spasms but don’t want to use muscle relaxers, some over-the-counter medications aren’t that strong and can help. For example, acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce pain, which helps to ease the severity of spasms.
The Bottom Line on Muscle Relaxers
Muscle relaxers are usually meant for short-term use to help you function while an injury or underlying condition is being treated. Even though these medications shouldn’t be harmful as long as you stick to the dose your doctor prescribes, you must understand how your body processes muscle relaxers before taking them.
Knowing the half-life of a medication ensures that you don’t take another dose while a considerable amount of the drug is still in your body. When you’re given a prescription for a muscle relaxer, make sure you use it responsibly. If you have questions about muscle relaxers, side effects, or addiction treatment, reach out to Live Free Recovery at (888) 527-1508 to speak with a member of our team.
References and Further Reading
- https://stillwatertreatment.com/how-long-does-flexeril-stay-in-your-system/
- https://www.drugs.com/medical-answers/how-long-does-flexeril-stay-in-your-system-374063/
- https://addictionresource.com/drugs/muscle-relaxers/how-long-stay-in-system/
- https://my.clevelandclinic.org/health/treatments/24686-muscle-relaxers
- https://www.healthcentral.com/condition/back-pain/muscle-relaxants-back-pain-neck-pain
- https://www.medicalnewstoday.com/articles/muscle-relaxers
- https://patient.info/bones-joints-muscles/muscle-relaxants
- https://www.rxlist.com/flexeril-drug.htm
If you’d like to learn more about muscle relaxers and their effects on the body, here are some suggestions for further reading:
- https://www.spine-health.com/blog/6-things-know-about-muscle-relaxants
- https://www.webmd.com/back-pain/do-i-need-a-muscle-relaxer
- https://www.healthline.com/health/muscle-relaxers
