How Long Do Muscle Relaxers Last? Factors & Medication Duration

Must relaxers are a type of highly predictable medications that provide relief for a window of between four and eight hours. That said, some extended-release formulations can last up to 24 hours before they’ve been largely metabolized.

Knowing how long each type of medication works is a crucial piece of the puzzle and can help you greatly reduce the risk of gaps in relief and, more importantly, overlap. In this post, we’re going to look at the typical durations of the most commonly prescribed muscle relaxers, so you can make more informed decisions with your healthcare provider to optimize your recovery outcomes.

Common Muscle Relaxers and Their Average Effective Durations

Methocarbamol (Robaxin)

Methocarbamol is the common name for the brand Robaxin. Robaxin will usually take effect in less than an hour and will help provide relief for up to six hours.[1] Patients will often start with a larger dose and follow that with a dose roughly half that every four to six hours after that, as needed.

Since the duration of methocarbamol isn’t very long, patients will find that for chronic or persistent spasms, they may be taking it three to four times per day to maintain consistent muscle relaxation. This also means it’s very important that patients should space doses evenly and avoid missing doses, since even one missed dose can lead to a lapse in relief and a rapid return of muscle cramping or spasms.[2]

Cyclobenzaprine (Flexeril)

Flexeril is the brand name for the generic drug cyclobenzaprine hydrochloride. Flexeril is a common skeletal muscle relaxant, and it will typically start working within an hour, while also providing relief for six to eight hours after that, with the immediate-release version. Patients will usually start around 5 to 10 mg once, or possibly twice daily, according to patient needs.[3] However, the extended-release effects of cyclobenzaprine can mean that a single capsule once daily is enough to keep muscles relaxed for 24 hours. It’s usually taken before bedtime or adjacent to activities that end up triggering muscle spasms or back pain.[4]

Since the immediate-release version wears off by the end of the day, patients who have ongoing or chronic muscle issues may determine that two doses each day are needed. It’s important to remember to space the doses evenly, so two doses would have twelve hours between them to maintain a constant level of relief. Missing a dose can lead to noticeable tension or cramp escalation, and doubling up a missed dose can lead to excessive drowsiness and other dangerous side effects.

Tizanidine (Zanaflex)

Tizanidine is sold under the brand name “Zanaflex”, and similarly to methocarbamol, it will typically take effect within an hour, although tizanidine will only relieve muscle spasms for six to eight hours, because it’s shorter half-life means it gets metabolized or broken down and flushed out faster than other short-term lower back pain treatments or skeletal muscle relaxants.[5]

While patients on prescription drugs like Zanaflex may find a compromise between extended-release formulations and short-acting formulations by only having to take a dose every six to eight hours, careful monitoring of blood pressure and liver function is critical to stay ahead of serious side effects.[6] Skipping doses can mean a rapid return of discomfort, but overdosing can lead to central nervous system depression, low blood pressure, and irregular heartbeat.

Primary Factors Impacting How Long Muscle Relaxers Last

There are dozens of factors that have the potential to impact how long muscle relaxers stay effective, but here we’ll look at the most common or significant factors. In other words, the ones you should pay the most attention to.

#1 – Metabolism & Age

Age is one of the most important factors in anything medical, and as a result, so is your metabolism.[7] Younger individuals have faster and more powerful metabolic processes, so drugs are broken down more quickly, leading to a shorter period of relief. As you advance in age, however, your metabolism slows down and becomes less efficient at breaking down everything from over-the-counter nonsteroidal anti-inflammatory drugs like acetaminophen to controlled substance prescriptions for muscle pain from fibromyalgia. Older adults will usually not need the same high doses or frequent dosing schedules as younger patients.

#2 – Dosage & Formulation

This is the trade-off between working fast and lasting long. Immediate-release tablets will deliver a rapid effect, but will always wear off quicker. On the other hand, extended-release formulations release the medication more slowly, or over a longer period, but typically take longer to kick in. Higher doses will not only extend the duration but also increase the risk of dangerous sedation and the likelihood of withdrawal symptoms when doses are missed.[8]

#3 – Liver and Kidney Function

Since most muscle relaxers are either metabolized by the liver or expelled by the kidneys, reduced organ function can mean it takes longer for your body to eliminate the drug.[9] This means patients with reduced renal function may experience prolonged drug levels, necessitating lower doses or less frequent dosing schedules.

#4 – Drug Interactions

There are countless combinations of prescription drugs, and many concomitant uses can inhibit or induce liver enzymes (like critical CYP450 isoforms), which can have dramatic effects on the active window of a muscle relaxer.[10] Anytime you have multiple prescriptions, you should obtain expert medical advice regarding potential interactions and conflicts to avoid unexpected changes in drug behavior or systemic response.

#5 – Individual Health & Body Weight

Drug effects are reduced with increased body mass, and individuals with higher mass will typically require higher doses than those with average weights, or more frequent dosing, to maintain the same blood concentration of the target substance.[11] At the same time, people with poorer health tend to eliminate drugs more slowly as well. Individual habits like hydration, nutrition, and activity can also have noticeable effects on the duration of muscle relaxers.

Find Hope and Relief In Professional Treatment

Getting a straight answer about how long muscle relaxers last and what can impact their duration is a powerful way to empower yourself to manage your muscle spasms or pain much more effectively and safely. Adhering closely to your healthcare provider’s prescribed dosing schedule, planning for the peak effects, and having open and honest communication with them about your care can help reduce risks.

If you have questions about your specific muscle relaxer regimen or are looking to explore specific alternative treatments, a trusted healthcare provider will be an excellent resource. If you or a loved one is struggling with addiction, reach out for practical support.

General Safety and Tapering Considerations

For anyone who may be taking or considering taking muscle relaxers, it’s important to know that long-term use, or high-dose use, will often lead to varying degrees of tolerance. This means that after taking it for a while, it’s going to take either larger doses or more frequent doses to give you the same relief.

Most of the common muscle relaxer medications also have a risk of physical dependence. Eventually, your body will adapt to them, and stopping suddenly can lead to rebound spasms, dry mouth, headaches, constipation, and other withdrawal effects.

Signs of Overuse

Pay attention to signs of overuse, like excessive sedation, persistent dizziness, or cognitive impairment that impacts daily function and living. If you’re taking an extra dose here and there just to “feel normal,” it’s time to talk to your healthcare provider about tapering your dose.

Tapering

One of the best ways to minimize withdrawal and rebound symptoms is to work with your medication team to gradually reduce your dose over days or weeks, instead of stopping cold turkey. This requires close collaboration with your healthcare team and strict adherence to the tapering schedule. In some cases you healthcare provider may encourage you to seek the help of a medical detox program.