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 that you don’t take another medication while the muscle relaxer is still active, you should know how long these medications remain in your body.
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Understanding Muscle Relaxers
Muscle relaxers are a category of prescription medications designed specifically to alter muscle function. Medical professionals prescribe these medications to treat many different symptoms, which extend to musculoskeletal pain, spasticity, and muscle spasms. Muscle relaxers can be separated into two distinct types, which include antispasmodics and antispasticity agents. Each type of muscle relaxer has its own applications and potential side effects.
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. As for antispastics, they are administered for the treatment of muscle spasticity, which is a symptom that involves tightness in the muscles.
Keep in mind that there aren’t any over-the-counter muscle relaxers in the U.S. These medications need to be prescribed by a healthcare professional. A few of the more commonly prescribed antispastics include:
Keep in mind that diazepam and tizanidine can be prescribed for antispastic and antispasmodic applications. The most commonly prescribed antispasmodics include:
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 them 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. A medication’s half-life is the amount of time it takes for the active substance to reduce in potency by half. The half-life for any medication depends on how your body processes and excretes it. It’s possible for the half-life of a drug to be anywhere from several minutes to a few weeks.
Half-life of Common Muscle Relaxers
Regardless of the symptom or condition you’re treating with muscle relaxers, you should know how long the medication remains in your system. The average half-life for muscle relaxers is:
- Cyclobenzaprine – Anywhere from eight hours to 36 hours
- Meprobamate – 10 hours with the potential for 48 hours with chronic use
- Atracurium – 20 minutes
- Vecuronium – 70 minutes
- Metocurine – 50 minutes
- Mivacurium – 10-20 minutes
- Rapacuronium – 10-20 minutes
For muscle relaxers like mivacurium, it has a short half-life as a result of it being metabolized by butyrylcholinesterase, which is synthesized in the liver. Excretion of these metabolites through the urine occurs after just 90 minutes. Doctors can determine the dosage a person should receive based on the half-life of a muscle relaxer.
For muscle relaxers like Flexeril, the drug should be fully out of your body in a period of 5.5-16.5 days. It has a lengthy half-life that can be anywhere between one to three days, which is the amount of time it takes for the plasma drug levels in your body to be reduced by half.
Factors Affecting Duration in the Body
There are many factors that determine how long muscle relaxers remain in your system, which 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:
- Baclofen – 72 hours for blood test, 48 hours for urine sample, 48-72 hours for saliva sample
- Soma – 24 hours for blood test, two to three days for urine sample, as long as four hours for saliva sample
- Flexeril – Up to 10 days for blood test, up to four days for urine sample, three to nine days for saliva sample
|Blood Test Detection Window
|Urine Sample Detection Window
|Saliva Sample Detection Window
|Two to three days
|Up to 4 hours
|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 the following:
- Drowsiness and fatigue
- Dry mouth
For specific medications like Flexeril, the most common side effects include:
- Stomach pain
- Blurry vision
- Loss of appetite
If you experience any of these side effects, you should speak with 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. Some of the signs that you or someone close to you is misusing muscle relaxers include:
- Continuing to use the medication after the treated symptoms are gone
- Sudden changes to sleeping habits
- Needing a larger dose to experience the same effects
- Faking muscle spasms or pain to receive medication
- Wanting to stop using muscle relaxers but being unable to do so
Muscle relaxers like diazepam and carisoprodol are controlled substances, which means that you can become dependent on them. Once your body is dependent on a drug, you can experience withdrawal symptoms when you attempt to stop taking it. You should also avoid consuming alcohol if you’re taking a muscle relaxer. Both substances are depressants, which will make your side effects considerably more intense. The symptoms you might go through if you take alcohol and muscle relaxers at the same time include:
- Blurry vision
- Low blood pressure
- Extreme dizziness or drowsiness
- Higher risk of overdose
- Liver damage
- Memory issues
An overdose on muscle relaxers can lead to such side effects as:
- Respiratory depression
- Cardiac arrest
Managing Muscle Relaxer Use
Regardless of the specific dosage and type of muscle relaxer you’re prescribed with, it’s crucial that you adhere to the prescribed dosage. If you take a higher dose or consume the medication more often than prescribed, you’ll be at a higher risk of becoming dependent on the substance.
When you experience side effects or find that your symptoms aren’t getting better, you should speak with your doctor. The same is true if you believe that you’re becoming dependent on muscle relaxers. 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, there are some over-the-counter medications that aren’t that strong and can help you treat muscle problems. For example, acetaminophen and nonsteroidal anti-inflammatory drugs can reduce muscle soreness and the severity of spasms.
Muscle relaxers are standard medications that are prescribed to people who may be suffering from muscle spasms or tightness. Even though these medications shouldn’t be harmful as long as you stick to the dose your doctor prescribes, it’s essential that you understand the pharmacokinetics of 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. Consult with healthcare providers if you have any questions about muscle relaxers and their side effects.
References and Further Reading
If you’d like to learn more about muscle relaxers and their effects on the body, here are some suggestions for further reading:
Published on: 2023-12-20
Updated on: 2023-12-20