Drug side effects
tizanidine Side Effects
The reactions most often reported to the FDA for tizanidine (also sold as Zanaflex), with demographics, serious outcomes, and reporting trends.
Data updated 2026-05-15
- 22,750
- FAERS reports
Data from the FDA Adverse Event Reporting System (FAERS), 2004 to 2025. A FAERS report records a temporal association, not proof of cause. See our methodology for how figures are compiled and de-duplicated.
The most commonly reported side effects of tizanidine come from 22,750 reports to the FDA, broken down here by frequency, patient demographics, and serious outcomes.
This page analyzes 22,750 reports to the FDA Adverse Event Reporting System (FAERS) for tizanidine (Zanaflex): the reactions reported most often, who reported them, serious outcomes such as hospitalization, and year-over-year trends. A FAERS report does not prove the drug caused the effect, and report volume tracks how widely a drug is used, not how likely an effect is for any one person. Educational information, not medical advice.
Total Reports
22,750
Reports Mentioning Death
1,739
7.6% of reports — not proof the medicine caused the death
Hospitalizations
6,474
28.5% of reports
Top Indication
Product Used For Unknown Indication
Most Reported Adverse Reactions
Who Reports Side Effects
Gender Distribution
Age Distribution
Reporting Trend by Year
Reactions in Death Reports
Top reactions reported in 1,739 reports where death was an outcome. These are voluntarily reported and do not establish causation.
| Reaction | Reports |
|---|---|
| DEATH | 499 |
| COMPLETED SUICIDE | 485 |
| TOXICITY TO VARIOUS AGENTS | 274 |
| CARDIO-RESPIRATORY ARREST | 129 |
| CARDIAC ARREST | 108 |
| SUSPECTED SUICIDE | 106 |
| ACUTE KIDNEY INJURY | 100 |
| CHRONIC KIDNEY DISEASE | 98 |
| RENAL FAILURE | 76 |
| RESPIRATORY ARREST | 72 |
| END STAGE RENAL DISEASE | 56 |
| PNEUMONIA | 47 |
| FALL | 44 |
| OVERDOSE | 38 |
| SEPTIC SHOCK | 36 |
| HYPOTENSION | 34 |
| ASTHENIA | 30 |
| DYSPNOEA | 29 |
| URINARY TRACT INFECTION | 29 |
Reactions in Hospitalization Reports
Top reactions in 6,474 reports where hospitalization was an outcome.
| Reaction | Reports |
|---|---|
| FALL | 598 |
| PAIN | 484 |
| NAUSEA | 480 |
| PNEUMONIA | 452 |
| URINARY TRACT INFECTION | 428 |
| FATIGUE | 424 |
| DYSPNOEA | 348 |
| ACUTE KIDNEY INJURY | 338 |
| HEADACHE | 337 |
| VOMITING | 337 |
| ASTHENIA | 325 |
| DIARRHOEA | 323 |
| HYPOTENSION | 323 |
| DIZZINESS | 299 |
| SOMNOLENCE | 299 |
| ARTHRALGIA | 257 |
| MULTIPLE SCLEROSIS RELAPSE | 252 |
| CHRONIC KIDNEY DISEASE | 248 |
Nearby, Related Medications
What the FAERS Data Reveals About tizanidine Side Effects
The FDA Adverse Event Reporting System (FAERS) contains 22,750 voluntary reports linked to tizanidine and its brand equivalents (Zanaflex), spanning 2004 through 2025. Of those, 1,739 (7.6%) listed death as an outcome and 6,474 (28.5%) involved hospitalization. The most common indication reported alongside adverse events was Product Used For Unknown Indication.
Demographic breakdowns help contextualize who is being exposed to the drug. Of reports with known sex, 75% were female and 25% male; age distribution skews toward 45-64, with 7,737 reports in that bracket. The single most reported reaction is fatigue with 1,693 submissions, followed by pain and nausea.
How to read these numbers
FAERS is a signal-detection tool, not a scorecard. Reports are voluntary, and a single case may list multiple suspect drugs, so numbers above should not be read as incidence rates or per-patient risk. Widely prescribed drugs naturally accumulate more reports than niche therapies even when individual risk is low. These aggregates are useful for spotting patterns that merit further pharmacovigilance, not for choosing between medications. This page is for educational reference only and is not medical advice, speak with a licensed clinician about any side-effect concerns.
Drugs With a Similar FAERS Report Volume
Other medications with a total FDA adverse-event report count closest to tizanidine's 22,750.
Read our methodology - how this data is sourced, computed, and verified.