Tizanidine Side Effects: Zanaflex Warnings and Precautions

Last Updated: October 11, 2021

Authored by Roger Weiss, MD

Reviewed by Michael Espelin APRN

Tizanidine is a prescription medicine commonly used in treating muscle spasticity by temporarily relaxing muscles. The Tizanidine oral tablet is usually known by the brand-name drug Zanaflex, although generic versions are readily available. Like any medication, using it regularly has fallbacks. Learn why it is prescribed, its health benefits, the typical and dangerous Tizanidine side effects, precautions, and how to deal with an overdose.

What Are the Common Tizanidine Side Effects?

Tizanidine uses usually involve treating muscle spasticity caused by multiple sclerosis, spinal cord injury. When taking Tizanidine, it is beneficial for one’s health to do so as directed. It is often available as an oral tablet or oral capsule. Therefore, it is convenient for patients, although substituting the tablets and capsules with each other should not be done.

Although it is an efficient drug for treating muscle spasms, patients might also experience some of its adverse effects. It is a short-acting medication. Thus it takes only 1 and 3 hours to notice its results and outcomes. The typical adverse outcomes of Zanaflex can be divided into short-term and long-term.

The Short-Term Tizanidine Side Effects Include:

  • Chills or fever
  • Chest pain
  • Burning or pain while urinating
  • Nausea or vomiting
  • Dizziness or drowsiness
  • Unusual tiredness
  • Diarrhea or constipation
  • Stomach pain
  • Dry mouth
  • Back pain
  • Muscle weakness
  • Sweating
Man is suffering from headache

Many of these adverse outcomes will go away as the body adjusts to the drugs during the treatment period. However, a doctor will also give information to the patient about reducing or even preventing some of these adverse effects, which can be long-term.

These Include:

  • Depression
  • Liver disease
  • Kidney disease
  • Weight gain
  • Joint pain

The list of possible Tizanidine side effects can look overwhelming; however, it is good to remember that only very few people experience these symptoms at all. Furthermore, if a medication is approved by the Food and Drug Administration, most people will tolerate it.

Which Are the Most Dangerous Side Effects Of Zanaflex?

As mentioned above, some of the effects of Zanaflex are commonplace and do not put the patient’s life in danger. But, unfortunately, there are some situations when the side effects of Zanaflex can be life-threatening.

Allergic Side Effects

Although only about 5 to 10% of adverse reactions to drugs are allergic, the patient should immediately call for an ambulance or go to the nearest emergency room at the first signs of a possible allergic reaction. For example, the patient might have an allergic reaction to Tizanidine, resulting in itching, vomiting, trouble breathing, anxiety, and even anaphylaxis leading to death. There may also be a rash, swelling of the face, hands, lips, tongue, or difficulty swallowing.

Side Effects With Other Medicines

One of the contraindications is combining it with medical prescriptions that can slow down breathing or cause sleepiness. Therefore, the patient should inform the doctor before taking prescription cough medicine, narcotic pain medicine, sleeping pills, medicine for seizures, depression or anxiety, or muscle relaxers.

Side Effects Involving the Heart

Tizanidine might cause an irregular heartbeat in some patients, known as QT prolongation, which can be life-threatening. The condition can cause seizures, fainting, and even sudden death. Thus, the patient should tell the doctor if they know themselves at risk for heart rhythm problems. Also, Zanaflex can cause tiredness, sleepiness, a delay in reactions, and lightheadedness, increasing the chances of mechanical failure, which can cause death.

Can Zanaflex Side Effects Cause Death?

As mentioned earlier, although people typically tolerate Tizanidine and find it relieving, there are still dangerous adverse effects to beware of since they can be life-threatening. These usually involve allergic reactions and heart trouble, such as slowing down the heart rate and reducing blood pressure.

Overdosing on it can also be fatal and even lead to coma. How toxic it depends on individual tolerance and the presence of other similar drugs. However, patients need to be careful when taking the medication; in a study of 523 homicidal poisonings, 65% involved medicines, including muscle relaxers.

What to Do in the Case of Tizanidine Overdose?

Taking multiple doses of Tizanidine can lead to overdose symptoms that include weakness, drowsiness, and confusion. Tizanidine overdose may be accidental or indented. Usually, when there is an overdose, certain medications can counter the toxic outcomes, but there is no known antidote for Tizanidine toxicity. However, the only dependable way to withdraw from an overdose is by using a medically supervised detoxification to properly decrease the medication while monitoring and treating acute adverse effects.

Suppose a patient is taking multiple doses of Tizanidine; it can lead to overdose symptoms that include weakness, drowsiness, and confusion. There can also be slow heart rate, shallow breathing, lightheadedness, or fainting. If these symptoms appear, those who overdosed or loved ones must seek the nearest emergency hospital services.

Woman is suffering from drug overdose

Tizanidine Pregnancy and Breastfeeding Warnings

The research on this medication used by pregnant women is limited. However, in some animal studies, the drugs caused congenital disabilities and other pregnancy problems. Hence, the US Food and Drugs Administration has placed Tizanidine in pregnancy category C.

It should only be used when the risks outweigh the benefits because of possible dangers. For instance, 35–50% of spinal cord injuries are due to motor vehicle accidents. Therefore, Tizanidine may be more beneficial than harmful and warrant use if a pregnant woman has such an injury despite potential risks.

In addition, it is not clear whether the drugs cross into breast milk, so safety has not been established. However, it is possible as it is lipid-soluble. Therefore, nursing parents should alert their physicians that they are breastfeeding before. However, Tizanidine oral tablet is not recommended. Nonetheless, if used, the nursing infant should be observed for toxicity such as low blood pressure, sedation, and hallucinations.

Variables That Affects Side Effects Emergence

All medications can cause side effects. However, most people experience no adverse effects or only minor ones. The likelihood of having negative effects from medicines depends on certain variables.

In some older people, the kidneys do not function properly. That means they process the drug more slowly, resulting in Zanaflex staying in the body for a longer time. In addition, the knock-on effect increases the risk of Zanaflex side effects; thus, the elderly should have the smallest effective doses.

Pre-existing Health Conditions

For instance, it occasionally causes liver injury. Thus if a patient has liver disease already, that can be dangerous. Also, if the patient has kidney disease, it can cause the medication to accumulate in the body.

Types of Intake

The medicine is available in different forms, tablets, and capsules. The capsules are often absorbed further in the digestive system and are less likely to cause symptoms such as dry mouth. Suppose the medication is taken with food or without. The patient can choose either option but should be consistent in administering Zanaflex and its dose.

Individual Tolerance

Every person is different. Therefore some people naturally get used to these medical pills faster than others.

Interactions With Other Substances

Combinations of medicines with others or substances such as alcohol can increase the effects. So not respecting the Tizanidine contraindications and combining it with other drugs can be dangerous.

Allergy to the Drug

It is typically rare to have a severe allergic reaction to any doses of Tizanidine. However, like individual tolerance, everyone differs. Suppose there’s any notice of symptoms such as swelling, trouble breathing, and severe dizziness. Then medical help is required.

Precautions to Prevent Side Effects Of Tizanidine

Asking the doctor for the correct information about the possible Tizanidine side effects from its doses can help the patient know what to expect from this drug and how to handle adverse reactions. Usually, when taking Tizanidine, the patient starts at the lowest possible amount. Then, the doctor gradually increases it after regular checkups.

Tizanidine Precautions on Digestion

On such checkups, the doctor should be informed right away if there are digestive system problems. These include dark urine, pale stools, pain in the upper stomach, nausea, vomiting, decreased appetite, or yellow skin or eyes. These might be signs of a severe liver problem.

Tizanidine Precautions on Muscles

Doses should be avoided when muscle tone is needed for safe balance and movement during certain activities. For example, it may be dangerous to have a relaxed muscle tone when driving. In addition, patients should discontinue any hazardous activity because of impaired reactions. Sudden movements can cause adverse effects of Zanaflex, such as lightheadedness, dizziness, or fainting.

Tizanidine Blood Pressure Precautions

Tizanidine blood pressure precautions are necessary because they might lead to a dangerous decrease in blood pressure, causing fainting or dizziness. That’s why the doctor will prescribe the lowest possible dose of Tizanidine to prevent this risk, which is still efficient for the patient. If the individual is already under treatment with drugs that lower blood pressure, they will need to be more attentive to their blood pressure charting. They should seek help if there are any concerning changes to their health.

 Tizanidine Weight Precautions

Does Tizanidine cause weight gain? It is possible. If there is weight gain, the doctor will keep a close eye by closely monitoring any change in weight and ask about exercise or eating habits. The doctor will also do a physical exam to get information about the difference in weight that does not have a particular cause, such as a pregnancy or retaining fluids. Suppose the drug causes weight gain, and it starts to affect the health of the individual. In that case, the doctor might recommend a different medicine to the patient.

Man with measuring tape

Key Information on Tizanidine

It is a muscle relaxant typically prescribed for use in multiple sclerosis, stroke, and spinal cord injuries. It is a short-acting medication with adverse short-term outcomes: chills or fever,  pain, nausea or vomiting, diarrhea, drowsiness, tiredness, and others. Also, adverse long-term side effects of Tizanidine include depression, liver disease, kidney disease, weight gain, and joint pain. Dangerous side effects of Tizanidine involve anaphylaxis or allergy, coma, and heart problems. Also, it is not recommended in pregnancy or when breastfeeding.

Tizanidine should be started with the lowest possible dose to prevent adverse effects, and regular checkups are also necessary. If the drug causes weight gain, which affects the individual’s health, the doctor recommends a different medicine. There are no Tizanidine headaches precautions; however, blood pressure, muscles, digestion, and weight should be observed while taking the medication.

Like many medications, Tizanidine is addictive over time or through deliberate misuse. Some people can get addicted to the drugs because it helps with insomnia, as a common side effect of the drug is sleepiness. It also helps with battling chronic pain. Thus, patients have to be wary since there can even be a Tizanidine overdose. If there is an addiction, Tizanidine is gradually weaned off with a reduced dose until it is stopped to avoid withdrawal symptoms in a step-down regiment at a rehab or detox center.

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Published on: February 19th, 2020

Updated on: October 11th, 2021

About Author

Roger Weiss, MD

Dr. Roger Weiss is a practicing mental health specialist at the hospital. Dr. Weiss combines his clinical practice and medical writing career since 2009. Apart from these activities, Dr. Weiss also delivers lectures for youth, former addicts, and everyone interested in topics such as substance abuse and treatment.

Medically Reviewed by

Michael Espelin APRN

8 years of nursing experience in wide variety of behavioral and addition settings that include adult inpatient and outpatient mental health services with substance use disorders, and geriatric long-term care and hospice care.  He has a particular interest in psychopharmacology, nutritional psychiatry, and alternative treatment options involving particular vitamins, dietary supplements, and administering auricular acupuncture.