Tizanidine
Also called Sirdalud, Ternelin, Zanaflex
Part of the metabolic pathway of Tizanidine. See the timeline on the metabolic highway.
Enzymes that break it down: CYP1A2. Wikipedia’s drug infobox says: “Extensive (>95%), primarily via CYP1A2” (revision 1369356605).
Dosage
Oral bands as drawn from PsychonautWiki's ranges below. The table is the source of truth.
Oral
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Duration
Mixing
For best safety practice, don't mix this drug with other depressants.
Why: respiratory depression. PsychonautWiki says:
- “Respiratory depression (also known as hypoventilation) can be described as a reduced urge to breathe that can be fatal depending on its intensity.” (PsychonautWiki, Respiratory depression, revision 150612)
- “... otherwise safe dosages of these compounds can become fatal when combined with even small amounts of other classes of depressant. For example, benzodiazepines combined with opioids are an extremely common cause of fatal respiratory depression. It is therefore strongly discouraged to combine these depressants at any dosage range.” (PsychonautWiki, Respiratory depression, revision 150612)
- “The most common cause of substance-related deaths is the combination of depressants (such as opiates, benzodiazepines, or alcohol) with other depressants.” (PsychonautWiki, Responsible drug use, revision 168206)
- “This combination potentiates the muscle relaxation, amnesia, sedation, and respiratory depression caused by one another. At higher doses, it can lead to a sudden, unexpected loss of consciousness along with a dangerous amount of depressed respiration.” (PsychonautWiki, dangerous interactions table, "Depressants" row, revision 156847)
Quotes from PsychonautWiki, CC BY-SA 4.0.
Acute combinations: what happens when these are taken close together. Entries backed by a medical journal or agency are listed first.
Backed by medical journals
PsychonautWiki also lists dangerous combinations shared across a whole group (depressants) in a table this page does not copy. Read that list on PsychonautWiki.
Risks and toxicity
It is strongly recommended that one use harm reduction practices when using this substance. PW
While no long term studies of tizanidine use in humans have been done, studies done in animals indicate no signs of long term carcinogenicity. However, tizanidine has been shown to have a developmental effect on young rats.[10] PW
Some long term tizanidine use has been attributed to liver problems and in extreme cases, liver failure and death.[11] PW
Lethal dosage
The LD50 of oral tizanidine in rats was found to be 414mg/kg in rats and 235 mg/kg in mice.[10] PW
In some cases, Tizanidine overdose can be reversed with naloxone; however, this is not the case with everyone.[12]
Tolerance and addiction potential
While dependence is rare, use of Tizanidine exceeding 36mg daily over an extended period of time can lead to hypertensive withdrawals. In cases where dependence has been built, a user should taper to avoid a hypertensive crisis.[14] PW
Testing
Effects
Overview
Tizanidine (known by the trade names Zanaflex and Trinex among others) is a depressant substance of the arylaminoimidazoline class closely related to clonidine. Tizanidine is primarily used primarily as an antispasmodic drug. Tizanidine's effectivness is similar to that of baclofen or diazepam.[1] PW
Tizanidine, sold under the brand names Zanaflex and Sirdalud among others, is an α₂-adrenergic receptor agonist and muscle relaxant which is used to treat muscle spasticity due to spinal cord injury, multiple sclerosis, and spastic cerebral palsy. Its effectiveness appears to be similar to that of other muscle relaxants like baclofen or diazepam. The drug is taken orally.[2–6] WP
Common side effects of tizanidine include sleepiness, dry mouth, asthenia, dizziness, low blood pressure, and low heart rate. Serious side effects may include dangerously low blood pressure, liver problems, and psychosis. It is unclear if use in pregnancy and breastfeeding is safe. The drug is an α₂-adrenergic receptor agonist, but how it works is not entirely clear.[2]
Tizanidine was approved for medical use in the United States in 1996. It is available as a generic medication. In 2023, it was the 81st most commonly prescribed medication in the United States, with more than 8 million prescriptions.[3]
History
History
Tizanidine was approved for medical use in the United States in 1996.[2] WP
Legal status
- Austria: Tizanidine is available by prescription only. PW
- Turkey: Tizanidine is available in pharmacies without prescription. PW
- United States: Tizanidine is available by prescription only. PW
- United Kingdom: Tizanidine is available by prescription only. PW
Names
Tizanidine is the generic name of the drug and its INN (International Nonproprietary Name), BAN (British Approved Name), and DCF (Dénomination Commune Française). In the case of the hydrochloride salt, its generic name is tizanidine hydrochloride and this is its USAN (United States Adopted Name) and BANM (British Approved Name). Developmental code names of tizanidine include AN-021 and DS 103-282 and its major brand names include Zanaflex and Sirdalud.[15–18] WP
Pharmacology
Pharmacodynamics
Tizanidine is an α₂-adrenergic receptor agonist and is closely related to clonidine. It has approximately one-tenth to one-fifteenth of the blood pressure-lowering effect or potency of clonidine. The relation between the α₂-adrenergic receptor agonism and spasmolytic action of tizanidine is still not fully understood.[4] WP
Absorption
Tizanidine is essentially completely absorbed with oral administration. The oral bioavailability of tizanidine is approximately 40%. It is subject to extensive first-pass metabolism and this is responsible for its incomplete bioavailability. The pharmacokinetics of tizanidine are linear across a dose range of 1 to 20 mg. The time to peak levels with tizanidine under fasting conditions is 1 hour and under fed conditions is 1.5 to 3 hours. The pharmacokinetics of tizanidine with oral tablet and capsule formulations are the same under fasting conditions but diverge and are non-equivalent under fed conditions. The pharmacokinetics of tizanidine also change when capsules are opened and it is sprinkled onto applesauce versus intact capsules.[2]
Distribution
Tizanidine is extensively distributed throughout the body. Its volume of distribution is 2.4 L/kg following intravenous injection. The drug's plasma protein binding is approximately 30%.[2]
Metabolism
More than 95% of a dose of tizanidine is metabolized. The primary cytochrome P450 enzyme involved in the metabolism of tizanidine is CYP1A2. Strong CYP3A4 inhibitors such as fluvoxamine and ciprofloxacin can increase tizanidine exposure by 10- to 33-fold, indicating the key involvement of CYP1A2 in the metabolism of the drug. The metabolites of tizanidine are thought to be inactive.[2] WP
Elimination
Tizanidine is eliminated 60% in urine and 20% in feces. Its elimination half-life is approximately 2.5 hours. The inactive metabolites of tizanidine have half-lives of 20 to 40 hours.[2] WP
Receptor binding · Wikipedia
Every row cites [19]
| col1 | col2 | col3 | col4 |
|---|---|---|---|
| α2A | 62 | Human | WP⚠ This row of the source table has a different number of cells than its headings, so columns may not line up. |
| α2B | 75 | OK | WP⚠ This row of the source table has a different number of cells than its headings, so columns may not line up. |
| α2C | 76 | Rat | WP⚠ This row of the source table has a different number of cells than its headings, so columns may not line up. |
Chemistry
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References
- Other Wagstaff AJ, Bryson HM. Tizanidine. A review of its pharmacology, clinical efficacy and tolerability in the management of spasticity associated with cerebral and spinal disorders. Drugs. 1997 Mar;53(3):435-52. doi: 10.2165/00003495-199753030-00007. PMID: 9074844
- Journal / agency Highlights of prescribing information - ZANAFLEX (tizanidine) capsules, for oral use
- Other British national formulary: BNF 76. 2018
- Other Katzung BG. Basic & clinical pharmacology. 30 November 2017
- Journal / agency Kamen L, Henney HR, Runyan JD. A practical overview of tizanidine use for spasticity secondary to multiple sclerosis, stroke, and spinal cord injury. Current Medical Research and Opinion. February 2008. doi:10.1185/030079908X261113 · PMID 18167175
- Other Tizanidine Hydrochloride Monograph for Professionals
- Other Tizanidine Pregnancy and Breastfeeding Warnings
- Other Kane SP. Top 300 of 2023
- Other Kane SP. Tizanidine Drug Usage Statistics, United States, 2014 - 2023
- Harm reduction site https://www.drugbank.ca/drugs/DB00697
- Journal / agency Clinical and Research Information on Drug-Induced Liver Injury [Internet]. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases; 2012-. Tizanidine. [Updated 2017 Jan 30]. Available from
- Other Bader D, Adam A, Shaban M, Alyahya B. Pediatric tizanidine toxicity reversed with naloxone: a case report. Int J Emerg Med. 2021 Dec 14;14(1):73. doi: 10.1186/s12245-021-00397-y. PMID: 34906071; PMCID: PMC8903539
- Other Spiller HA, Bosse GM, Adamson LA. Retrospective review of Tizanidine (Zanaflex) overdose. J Toxicol Clin Toxicol. 2004;42(5):593-6. doi: 10.1081/clt-200026978. PMID: 15462150
- Other Tizanidine Hydrochloride Monograph for Professionals". Drugs.com. American Society of Health-System Pharmacists. Retrieved 3 March 2019
- Journal / agency Tizanidine
- Other Elks, J. The Dictionary of Drugs: Chemical Data: Chemical Data, Structures and Bibliographies. 14 November 2014
- Other Index Nominum 2000: International Drug Directory. 2000
- Journal / agency Tizanidine. 16 April 2026
- Journal / agency Blaxall HS, Murphy TJ, Baker JC, Ray C, Bylund DB. Characterization of the alpha-2C adrenergic receptor subtype in the opossum kidney and in the OK cell line. The Journal of Pharmacology and Experimental Therapeutics. October 1991. doi:10.1016/S0022-3565(25)20309-3 · PMID 1656026
- Journal / agency Tizanidine: MedlinePlus Drug Information
- Other Zanaflex (tizanidine hydrochloride) Capsules and Tablets for Oral Use. Full Prescribing Information
Text and values on this page are quoted from PsychonautWiki (CC BY-SA 4.0), Wikipedia (CC BY-SA 4.0), PubChem (public domain). Each value links to the exact revision it came from.