Medication Guide App

Zanaflex Side Effects

Generic Name: tizanidine

Note: This page contains side effects data for the generic drug tizanidine. It is possible that some of the dosage forms included below may not apply to the brand name Zanaflex.

It is possible that some side effects of Zanaflex may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to tizanidine: oral capsule, oral tablet

As well as its needed effects, tizanidine (the active ingredient contained in Zanaflex) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking tizanidine, check with your doctor immediately:

More common
  • Chest pain or discomfort
  • fever or chills
  • nausea or vomiting
  • nervousness
  • pain or burning while urinating
  • unusual tiredness
Less common
  • Blurred vision
  • flu-like symptoms
  • irregular heartbeat
  • itching skin
  • kidney stones
  • right upper stomach tenderness
  • seeing things that are not there
  • shortness of breath
  • weight gain
Incidence not known
  • Continuing vomiting
  • general feeling of tiredness or weakness
  • headache
  • light-colored stools

If any of the following symptoms of overdose occur while taking tizanidine, get emergency help immediately:

Symptoms of overdose
  • Blurred vision
  • change in consciousness
  • chest pain or discomfort
  • confusion
  • decreased awareness or responsiveness
  • difficult or troubled breathing
  • dizziness, faintness or lightheadedness when getting up from a lying position
  • irregular, fast or slow, or shallow breathing
  • lightheadedness, dizziness, or fainting
  • loss of consciousness
  • pale or blue lips, fingernails, or skin
  • severe sleepiness
  • sleepiness or unusual drowsiness
  • slow or irregular heartbeat
  • sweating
  • unusual tiredness or weakness

Some tizanidine side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

More common
  • Dizziness or lightheadedness, especially when getting up from a lying or sitting position
  • drowsiness
  • dry mouth
  • fatigue
  • sleepiness
  • weakness
Less common
  • Constipation
  • nervousness
  • sore throat

For Healthcare Professionals

Applies to tizanidine: oral capsule, oral tablet

Nervous system

Visual hallucinations were observed in 3% (n=5) of patients in 2 clinical trials. Patients were aware the events were not real in most cases, and in only one case did problems persist following discontinuation. Sedation appears to be dose related in single dose studies and may in approximately 10% of cases be severe enough to interfere with daily activities. In multiple dose studies, however, the incidence of sedation peaked following one week of treatment, and remained stable thereafter.

Nervous system side effects have frequently been associated with the use of this tizanidine. Sedation, somnolence, and asthenia have been reported in up to 48% of patients. Dizziness has been reported in 16% of patients. Duskiness, hallucinations, nervousness, insomnia, and speech disorder have been reported rarely.

Gastrointestinal

Gastrointestinal side effects have included dry mouth in approximately 50% and constipation or vomiting in less than 4% of patients.

Hepatic

Most cases of elevated liver function tests in patients receiving tizanidine (the active ingredient contained in Zanaflex) rapidly resolved upon removal of the medication. Of the three deaths reported, two patients had symptoms of liver disease following 2 months of treatment while one occurred following 11 days. Two of the patients were receiving other medications that have been associated with hepatic toxicity.

Hepatic side effects associated with the use of tizanidine have included elevations of liver function tests to greater than 3 times the upper normal limit in 5% of patients. Three deaths associated with liver failure have been reported during postmarketing surveillance in patients receiving tizanidine.

Cardiovascular

Cardiovascular side effects have included hypotension and bradycardia. Rarely, severe hypotension associated with use of this drug has required IV fluids, epinephrine, and dopamine.

The manufacturer reports a single dose study that found hypotension in 16% and 30% of patients following an 8 and 16 mg dose, respectively. The occurrence of bradycardia under the same circumstances was 2% and 10%.

Ocular

Ocular side effects including blurred vision have been reported rarely.

Dermatologic

Dermatologic side effects have been isolated to rashes.

Other

Other side effects have included three cases of rebound symptoms on sudden withdrawal of tizanidine (the active ingredient contained in Zanaflex) Withdrawal symptoms included hypertension, tachycardia, hypertonia, tremor, and anxiety.

The withdrawal case reports suggested that these patients were also misusing narcotics.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. Drugs.com does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.

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