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Side Effects of Muscle Relaxers: What to Expect and When to Call

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Muscle relaxers most often cause drowsiness, dizziness, fatigue, nausea, headache and dry mouth. Serious reactions are rarer but real: confusion, hallucinations, seizures, a racing heartbeat, and dangerous breathing problems when the drugs are mixed with alcohol or opioids. If you need relaxers again and again, that pattern is worth taking to your doctor, because it can mean the cause of your pain has not been found. This guide covers each drug’s side effects, what makes them worse, how long they last and what to do next.

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TL;DR

  • Drowsiness, dizziness, fatigue, nausea, headache and dry mouth are the usual side effects, and they tend to fade as the dose wears off.
  • Alcohol, opioids and some other medicines can turn a mild side effect into an emergency. Never combine them without your prescriber’s approval.
  • Some relaxers, such as carisoprodol, tizanidine and baclofen, should not be stopped abruptly after prolonged use.
  • Relaxers are meant for short-term use. If you keep needing them, ask your doctor about finding the underlying driver of your pain, including immune system factors.
  • Chest pain, trouble breathing, hallucinations, seizures or swelling of the face or tongue need emergency care.

Table of Contents

The most common side effects of muscle relaxers

The side effects people report most are drowsiness and fatigue, dizziness, nausea, headache and dry mouth, according to Cleveland Clinic’s overview of muscle relaxers. Most relaxers act on the central nervous system, which is why sedation sits at the top of the list.

The numbers back this up. In trials of people with acute low back pain, skeletal muscle relaxers raised the risk of any adverse effect by about 50% (relative risk 1.50) compared with placebo. The risk of central nervous system effects such as dizziness and drowsiness roughly doubled (relative risk 2.04), as summarized by the American Academy of Family Physicians.

Each drug has its own profile:

Medicine Commonly reported effects Source
Carisoprodol Drowsiness (13 to 17%), dizziness (7 to 8%), plus tremor, agitation, irritability, insomnia and headache (each 3 to 5%) WHO critical review
Baclofen Headache, dry mouth, tiredness or weakness, dizziness or fainting, nausea or vomiting, eyesight problems, mood changes NHS
Cyclobenzaprine Drowsiness, dry mouth, dizziness; serious reactions listed below MedlinePlus

Other reviews describe sedation, headaches, blurred vision and dependency as effects to expect with skeletal muscle relaxers. A peer-reviewed review of appropriate use also notes that carisoprodol appears on the Beers list of medicines to use with caution in older adults.

Practical precautions for everyday effects

The NHS advises against driving, cycling or using machinery until baclofen’s dizziness, drowsiness and vision problems pass. The same common-sense rule applies to any relaxer that makes you sleepy. Take the first dose at a time when you can stay home, and see how you respond before you plan a commute, childcare or a ladder.

Because these drugs reduce muscle tone, the University of Michigan’s pain guide warns they can be risky if you depend on that tone for balance and movement. If you feel unsteady, tell your prescriber.

Serious side effects that need medical attention

Most side effects are a nuisance. Some are not. Contact a doctor or emergency service right away if you notice any of the following.

With cyclobenzaprine, MedlinePlus lists rash, itching, hives, swelling of the face or tongue, and difficulty breathing or swallowing. It also lists agitation, fever, sweating, confusion, fast or irregular heartbeat, shivering, severe muscle stiffness or twitching, hallucinations, loss of coordination, and chest pain.

With baclofen, MedlinePlus says to contact a doctor immediately for hallucinations (seeing things or hearing voices that are not there) and seizures.

With carisoprodol, high doses, whether taken by mistake or on purpose, can cause euphoria, hypomania, confusion, disorientation, muscle jerks, agitation and partial amnesia. Very high doses can cause respiratory failure, coma and death, according to the UK Advisory Council on the Misuse of Drugs. The safest approach is to take exactly the dose on your label and never double up after a missed dose.

If you or someone near you has taken too much, call 911 or Poison Control at 1-800-222-1222.

Serious side effects that need medical attention

What makes side effects stronger or more dangerous

Alcohol and opioids

Alcohol and muscle relaxers are both central nervous system depressants. Cleveland Clinic states that together they can cause extreme dizziness and drowsiness, blurred vision, low blood pressure, fainting, memory problems, liver damage and a higher risk of overdose. The University of Michigan says the same about combining relaxers with opioids: the effects add up, and the mix is particularly dangerous.

North Carolina Poison Control adds that combining relaxers with other medicines or alcohol, or taking an overdose, can lead to seizures, irregular heartbeat, low blood pressure, slow or shallow breathing, coma, heart attack and death.

Specific drug interactions

Tizanidine is the clearest example. A professional monograph states that taking it with fluvoxamine or ciprofloxacin is contraindicated because blood levels rise substantially and the blood-pressure-lowering and sedating effects grow. The same monograph reports that alcohol raised tizanidine exposure by about 20% and peak levels by about 15%. It also notes that pairing tizanidine with another antispasticity drug such as baclofen can cause additive sedation.

Give your pharmacist and prescriber a full list of everything you take, including over-the-counter products and supplements, before you start any relaxer.

Age, liver and kidney function

Your body’s ability to clear the drug matters. The cyclobenzaprine product monograph states that plasma concentrations are generally higher in older adults and in people with liver impairment. Tell your doctor if you have liver or kidney disease, or if you are over 65, so the dose can be chosen accordingly.

Can side effects last into the next day?

Yes, for some drugs. Cyclobenzaprine’s effective half-life is about 18 hours, with a range of 8 to 37 hours, according to its product monograph. That is why a bedtime dose can leave some people foggy or slow the next morning. The same document says it should be used only for short periods, up to two or three weeks.

Carisoprodol works faster and for a shorter time. The DEA reports that its effects last 4 to 6 hours and that the liver converts it to meprobamate. So the length of a side effect depends on the drug, your dose, your age and your liver. If next-day grogginess is affecting your driving or work, tell your prescriber. Do not just skip doses or add coffee and carry on.

Can side effects last into the next day?

Dependence and withdrawal

Not every relaxer carries the same risk, but several need a careful exit.

  • Carisoprodol: prolonged or excessive use can lead to dependence. Stopping abruptly after long use can cause anxiety, insomnia, tremors and muscle twitching, and in severe cases hallucinations and seizures, according to the WHO. It is a Schedule IV controlled substance in the US, and the DEA notes that continued misuse causes tolerance and dependence.
  • Tizanidine: sudden discontinuation may trigger a hyperadrenergic syndrome with fast heart rate, high blood pressure, tremor, anxiety and muscle tightness. A published review describes a case in which stopping it abruptly alongside baclofen led to delirium and autonomic dysfunction in a patient with impaired kidney function.
  • In general: the University of Michigan notes that many relaxers should be tapered slowly rather than stopped suddenly.

If you have been taking a relaxer daily for more than a few weeks, ask your prescriber for a taper plan before you stop.

How to choose and use a relaxer well

The evidence does not show that one relaxer is clearly better than another. The AFP says the choice should rest on side-effect profile, patient preference, abuse potential and possible drug interactions. That gives you a useful checklist for the appointment:

  1. Name your risks. Do you drive for work, drink alcohol, take opioids, antidepressants or antibiotics, or have liver or kidney trouble?
  2. Ask about the lowest effective dose and how long you should take it.
  3. Ask when to take it. Evening dosing suits some people who feel sleepy.
  4. Agree on an exit plan. Know whether you can stop at once or need to taper.
  5. Set a review date. If pain is still limiting you at that date, the conversation should move from the drug to the cause.

The same review that describes relaxer risks notes that physical therapy and adjunctive analgesics may be needed to prevent chronic use. Some patients also ask about other approaches to spasm. If that is you, cannabis for muscle spasms is one topic to raise with a licensed clinician, who can weigh it against your medical history and any medicines you take.

When you keep needing relaxers, look at the cause

A muscle relaxer treats a symptom: tight, spasming muscle. It does not tell you why the muscle is tight or why the pain keeps returning. If you have been through repeated prescriptions and the pain returns each time the drug wears off, you are in the group most likely to be told to try something else without a clear reason why.

Persistent pain can have many drivers. Posture, injury and nerve irritation are the familiar ones. Immune system activity is a less familiar one, and it is often not checked. Our article on why pain relief stops working walks through the reasons a treatment can fail and what to ask next. If your pain is concentrated in the lower back, our guide to lower back ache in women covers warning signs and causes worth discussing with your doctor.

What helps most at that point is objective information to take into the room, not another trial-and-error prescription.

Our perspective

Side effects are the price many people pay for short-term relief, and for a sore back after a strain, a short course can be a reasonable choice. The trouble begins when the same prescription is renewed for months because nobody has identified what keeps the pain going.

We built our work around one idea: chronic pain deserves objective data, not guesswork. The Pain Signal Test™ looks at immune system markers linked to pain through a simple blood draw. It rests on peer-reviewed DNA research from a leading U.S. university, and it addresses a factor in chronic pain that is often overlooked.

Results give you and your healthcare provider a shared, biological starting point for deciding what to do next. That means better questions at your appointment, and a clearer path than one more round of sedating pills.

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Getting a clearer answer with The Pain Signal Test™

If you have lived with pain long enough that relaxers, rest and over-the-counter options no longer settle it, The Pain Signal Test™ is built for that situation. It is a blood test that measures immune system markers associated with chronic pain, and it provides results you and your healthcare provider can use to discuss and chart next steps.

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Cost is a common worry. Patients typically pay nothing out of pocket when they are covered by Medicare or a PPO plan, and coverage can be verified before you order. Payment can also be made out of pocket or with FSA or HSA pre-tax medical funds. Visit The Pain Signal Test™ page to start.

FAQ

What side effects can cyclobenzaprine cause the next day?

Drowsiness, dizziness and mental fogginess can carry over because cyclobenzaprine’s effective half-life is about 18 hours, with a range of 8 to 37 hours. Older adults and people with liver problems tend to have higher blood levels. Avoid driving until you know how it affects you, and ask your prescriber about timing and dose.

Do muscle relaxers make you sleepy?

Yes, drowsiness is among the most common effects. Most relaxers act on the central nervous system, and Cleveland Clinic lists drowsiness and fatigue first. Alcohol or opioids make sleepiness much stronger and are dangerous together with relaxers.

Can you stop muscle relaxers suddenly?

Not always. After prolonged use, stopping carisoprodol abruptly can cause withdrawal such as anxiety, insomnia, tremors and, in severe cases, seizures. Stopping tizanidine suddenly can cause a rapid heart rate and high blood pressure. Ask your prescriber for a taper plan.

Which side effects mean I should get help right away?

Swelling of the face or tongue, trouble breathing or swallowing, chest pain, a fast or irregular heartbeat, hallucinations, seizures and severe confusion all need emergency care. Call 911. For a suspected overdose, call Poison Control at 1-800-222-1222.

What if I keep needing muscle relaxers for the same pain?

Tell your doctor, because repeated need suggests the cause of the pain is still unexplained. Ask whether further testing is appropriate. The Pain Signal Test™ measures immune system markers linked to chronic pain and gives you results to discuss with your provider.

Sources