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Zanaflex Side Effects Center
Medical Editor: Melissa Conrad Stöppler, MD
Zanaflex (tizanidine) is a muscle relaxant used to treat muscle tightness and cramping (spasm) caused by conditions such as multiple sclerosis or spinal injury. Side effects of Zanaflex may include:
- numbness or tingling,
- stomach pain,
- dry mouth,
- muscle weakness,
- back pain,
- increased muscle tone or spasms,
- skin rash, and
The recommended starting dose of Zanaflex is 2 mg. Dosage of Zanaflex can be gradually increased by 2 mg to 4 mg at each dose, with 1 to 4 days between dosage increases, until a satisfactory reduction of muscle tone is achieved. Zanaflex may interact with alcohol, acyclovir, cimetidine, amotidine, ticlopidine, zileuton, birth control pills, antibiotics, blood pressure medications, or heart rhythm medications. Tell your doctor all medications and supplements you use. Tell your doctor if you are pregnant or plan to become pregnant during treatment with Zanaflex; it may harm a fetus. It is unknown if Zanaflex passes into breast milk or if it could harm a nursing baby. Consult your doctor before breastfeeding. Zanaflex may cause withdrawal reactions, especially if it has been used regularly for a long time or in high doses.
Our Zanaflex Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
What is Patient Information in Detail?
Easy-to-read and understand detailed drug information and pill images for the patient or caregiver from Cerner Multum.
Zanaflex in Detail - Patient Information: Side Effects
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have any of these serious side effects:
- feeling light-headed, fainting, slow heart rate;
- hallucinations, confusion, unusual thoughts or behavior;
- nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); or
- burning or pain when you urinate.
Less serious side effects may be more likely to occur, such as:
- drowsiness or dizziness;
- feeling anxious or nervous;
- numbness or tingling;
- stomach pain, diarrhea, constipation, vomiting;
- dry mouth;
- muscle weakness, back pain;
- increased muscle tone or spasms; or
- sweating or skin rash.
This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect. You may report side effects to FDA at 1-800-FDA-1088.
Read the entire detailed patient monograph for Zanaflex (Tizanidine)
What is Patient Information Overview?
A concise overview of the drug for the patient or caregiver from First DataBank.
Zanaflex Overview - Patient Information: Side Effects
To relieve dry mouth, suck (sugarless) hard candy or ice chips, chew (sugarless) gum, drink water, or use a saliva substitute.
To reduce the risk of dizziness and lightheadedness, get up slowly when rising from a sitting or lying position.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
Tell your doctor right away if you have any serious side effects, including: fainting, mental/mood changes (such as hallucinations), slow/irregular heartbeat, vision changes (such as blurred vision).
Tizanidine has infrequently caused very serious (rarely fatal) liver disease. Tell your doctor immediately if you develop symptoms of liver disease, including: persistent nausea/vomiting, severe stomach/abdominal pain, dark urine, yellowing eyes/skin.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
In the US -
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.
Read the entire patient information overview for Zanaflex (Tizanidine)
What is Prescribing information?
The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.
Zanaflex FDA Prescribing Information: Side Effects
The following adverse reactions are described elsewhere in other sections of the prescribing information:
- Hypotension [see WARNINGS AND PRECAUTIONS]
- Liver Injury [see WARNINGS AND PRECAUTIONS]
- Sedation [see WARNINGS AND PRECAUTIONS]
- Hallucinosis/Psychotic-Like Symptoms [see WARNINGS AND PRECAUTIONS]
- Hypersensitivity Reactions [see WARNINGS AND PRECAUTIONS]
Clinical Trials Experience
Because clinical studies are conducted under widely varying conditions, adverse reaction rates observed in the clinical studies of a drug cannot be directly compared to rates in the clinical studies of another drug and may not reflect the rates observed in clinical practice.
Three double-blind, randomized, placebo controlled -clinical studies were conducted to evaluate the effect of tizanidine on spasticity control. Two studies were conducted in patients with multiple sclerosis and one in patients with spinal cord injury. Each study had a 13-week active treatment period which included a 3-week titration phase to the maximum tolerated dose up to 36 mg/day in three divided doses, a 9-week plateau phase where the dose of tizanidine was held constant and a 1- week dose tapering. In all, 264 patients received tizanidine and 261 patients received placebo. Across the three studies patient ages ranged from 15-69 years and 51.4 percent were women. The median dose during the plateau phase ranged from 20-28 mg/day.
The most frequent adverse reactions reported in multiple dose, placebo-controlled clinical studies involving 264 patients with spasticity were dry mouth, somnolence/sedation, asthenia (weakness, fatigue and/or tiredness) and dizziness. Three-quarters of the patients rated the events as mild to moderate and one-quarter of the patients rated the events as being severe. These events appeared to be dose related.
Table 1 lists signs and symptoms that were reported in greater than 2% of patients in three multiple dose, placebo-controlled studies who received Zanaflex where the frequency in the Zanaflex group was greater than the placebo group. For comparison purposes, the corresponding frequency of the event (per 100 patients) among placebo treated patients is also provided.
Table 1: Multiple Dose, Placebo-Controlled Studies-Frequent
( > 2%) Adverse Reactions Reported for Which Zanaflex Tablets Incidence is
Greater than Placebo
N = 261
N = 264
|Liver test abnormality||2||6|
|Amblyopia (blurred vision)||< 1||3|
|*(weakness, fatigue, and/or tiredness)|
In the single dose, placebo-controlled study involving 142 patients with spasticity due to multiple sclerosis (Study 1) [see Clinical Studies], the patients were specifically asked if they had experienced any of the four most common adverse reactions: dry mouth, somnolence (drowsiness), asthenia (weakness, fatigue and/or tiredness) and dizziness. In addition, hypotension and bradycardia were observed. The occurrence of these reactions is summarized in Table 2. Other events were, in general, reported at a rate of 2% or less.
Table 2: Single Dose, Placebo-Controlled Study-Common
Adverse Reactions Reported
N = 48
|Zanaflex Tablet, 8mg,
N = 45
N = 49
|*(weakness, fatigue, and/or tiredness)|
The following adverse reactions have been identified during post approval use of Zanaflex. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
Certain events, such as somnolence, dry mouth, hypotension, decreased blood pressure, bradycardia, dizziness, weakness or asthenia, muscle spasms, hallucinations, fatigue, liver function test abnormality and hepatotoxicity, have been observed in post marketing and clinical trials and are discussed in previous sections of this document.
The following adverse reactions have been identified as occurring in the post marketing experience of Zanaflex. Based on the information provided regarding these reactions, a causal relationship with Zanaflex cannot be entirely excluded. The events are listed in order of decreasing clinical significance; severity in the post marketing setting is not reported.
- Stevens Johnson Syndrome
- Anaphylactic Reaction
- Exfoliative Dermatitis
- Ventricular Tachycardia
Read the entire FDA prescribing information for Zanaflex (Tizanidine)
Additional Zanaflex Information
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Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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