Tizanidine: uses, dosing, side effects & brands

Ontralfy contains tizanidine hydrochloride as the active ingredient, which is a central alpha2-adrenergic agonist.

The FDA classifies tizanidine as a central alpha-2 adrenergic agonist. These drugs activate alpha-2 receptors in the brainstem, which tells the nervous system to send out less norepinephrine and reduce sympathetic (fight-or-flight) signaling to the body. With less of this stimulation, blood vessels relax and heart rate slows, lowering blood pressure. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.

The elimination half-life of tizanidine is about 2.5 hours — that is how long the body takes to clear half of a dose. Tizanidine's own metabolites are not known to be active, though they linger longer than the parent (half-lives of 20 to 40 hours); it is not a prodrug. Kinetics are dose-linear over 1 to 20 mg. The drug lasts longer in some people: clearance drops more than 50% when kidney function is reduced (creatinine clearance under 25 mL/min), and elderly patients clear it roughly 4 times more slowly than younger adults. Hepatic impairment was not formally studied but is expected to raise levels since tizanidine is extensively metabolized by the liver (via CYP1A2). Strong CYP1A2 inhibitors such as fluvoxamine and ciprofloxacin are contraindicated because they sharply increase tizanidine exposure. Half-life is not the same as how long a drug test can detect the drug, and it varies with age, kidney and liver function.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run tizanidine against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

We track 3 tizanidine-containing products in the U.S.: Ontralfy, Tizanidine Hydrochloride and Zanaflex. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.

Across the brands we track, tizanidine is currently marketed as solution, capsule and tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

Yes. Our catalog lists 1 generic tizanidine product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.

The FDA's Enforcement database lists 1 recall record whose product description mentions tizanidine. The most recent: Tizanidine Tablets (Jan 2, 2024). A recall applies to specific lots, not to the drug as a whole — check the record for the affected lot numbers.

Tizanidine is short-acting and starts working quickly: muscle-tone relief usually begins within about an hour and peaks around 1 to 2 hours after a dose, then wears off within a few hours. Because the effect is brief, it's dosed for the times you most need relief rather than kept steady around the clock. Drowsiness and a drop in blood pressure can appear as it peaks.

No. Tizanidine (Zanaflex) is a muscle relaxant that works on alpha-2 receptors; it is not an opioid and is not a DEA-scheduled controlled substance. It can cause drowsiness and a drop in blood pressure, and should not be stopped abruptly after long-term use.

The most common side effects of Zanaflex (tizanidine) are drowsiness (often pronounced), dry mouth, dizziness, and weakness or unusual tiredness. Because tizanidine is an alpha-2 adrenergic agonist, it can also lower blood pressure, so lightheadedness when standing up quickly is common, especially when you first start or after a dose increase. MedlinePlus also lists nervousness, vomiting, and constipation. Do not drive or operate machinery until you know how sedating it is for you.

Get emergency help if you have signs of a severe drop in blood pressure or fainting — the FDA label notes tizanidine "can produce hypotension" and that "Syncope has been reported in the post marketing setting." Call your doctor right away for signs of liver injury; the label warns Zanaflex "may cause hepatocellular liver injury," and MedlinePlus flags "pain in the upper right part of the stomach, yellowing of the skin or eyes," extreme tiredness, loss of appetite, or flu-like symptoms. Hallucinations are a defined risk: the label reports "Formed, visual hallucinations or delusions have been reported in 5 of 170 patients (3%)" in controlled studies — MedlinePlus describes this as "seeing things or hearing voices that do not exist." Also seek care for a very slow heartbeat, or any rash, hives, or swelling of the face, throat, tongue, or lips with trouble breathing or swallowing. This is not a complete list.

Zanaflex (tizanidine) is contraindicated — meaning it must not be used — with the strong CYP1A2 inhibitors ciprofloxacin (an antibiotic) and fluvoxamine (an antidepressant), because they block the enzyme that clears tizanidine and cause its blood levels to soar. The FDA label reports that with fluvoxamine, tizanidine "Cmax, AUC, and half-life... increased by 12-fold, 33-fold, and 3-fold, respectively," and with ciprofloxacin, Cmax and AUC "increased by 7-fold and 10-fold." The label states these changes "resulted in significantly decreased blood pressure, increased drowsiness, and increased psychomotor impairment." Tell any prescriber you take tizanidine before starting a new antibiotic or antidepressant.

No — do not stop Zanaflex (tizanidine) abruptly on your own. The FDA label warns that "Withdrawal adverse reactions include rebound hypertension, tachycardia, and hypertonia" — meaning your blood pressure and heart rate can rebound sharply and muscle tightness can return. MedlinePlus puts it plainly: "If you suddenly stop taking tizanidine, your heart may beat faster and you may have increased blood pressure or tightness in your muscles." If you and your doctor decide to stop, especially after long-term or higher-dose use, the dose should be tapered gradually under medical supervision rather than stopped at once.

Zanaflex (tizanidine) is short-acting and works within an hour or two of a dose, so drowsiness, dry mouth, and the blood-pressure-lowering effect tend to peak in the first few hours and then wear off — which is why it is usually dosed only when needed and up to three times a day, not around the clock. Sedation and dizziness are often strongest when you first start and after each dose increase, and many people find they ease as the body adjusts. Serious problems like liver injury or hallucinations can appear later during treatment, so keep scheduled follow-ups and liver-function checks. This is not a complete list of effects or timelines — ask your prescriber or pharmacist about your specific dose.

Tizanidine is FDA-approved to manage spasticity — the muscle tightness and involuntary spasms caused by conditions like multiple sclerosis and spinal cord injury. It's an alpha-2 agonist that calms overactive nerve signals to the muscles. Because its effect is short-lived, it's usually timed for the moments when relief matters most, such as before activity, rather than taken around the clock.

It is. Beyond its approved use for spasticity, tizanidine is prescribed off-label as a general muscle relaxant for acute low back or neck muscle spasm and sometimes for chronic tension-type or migraine headache prevention. These uses are not FDA-approved. Tizanidine can lower blood pressure and cause marked drowsiness, and it has important interactions — combining it with the antibiotic ciprofloxacin or the antidepressant fluvoxamine is contraindicated because they sharply raise tizanidine levels.