Tizanidine, a muscle relaxant prescribed for spasticity and muscle tightness, causes side effects in a significant number of people who take it. The most common are drowsiness, dry mouth, dizziness, and weakness. Most side effects are dose-dependent, meaning they get worse at higher doses, and they tend to be strongest in the first few hours after taking the medication. But tizanidine also carries some less obvious risks, including effects on blood pressure, liver function, and even perception, that are worth understanding before you start or adjust your dose.
The Most Common Side Effects
Drowsiness is the side effect you’re most likely to notice. Tizanidine works by calming nerve signals in the spinal cord that cause muscles to tighten, but it also dampens activity in the brain more broadly. The sedation can be strong enough to interfere with driving, working, or even holding a conversation, especially when you first start taking it or increase your dose. This effect gets significantly worse if you combine tizanidine with alcohol, benzodiazepines, opioids, or tricyclic antidepressants.
Dry mouth is another frequent complaint. It can range from mildly annoying to uncomfortable enough that it affects eating and speaking. Dizziness and general weakness round out the top four side effects. All of these tend to be more pronounced at higher doses, so many prescribers start low and increase gradually to find the smallest effective amount.
Blood Pressure Drops
Tizanidine is chemically similar to clonidine, a blood pressure medication, so it can lower your blood pressure in ways you might not expect from a muscle relaxant. The drop can happen in both systolic and diastolic pressure, sometimes enough to cause lightheadedness or fainting when you stand up quickly. Fainting episodes have been reported even after the drug went to market, not just in clinical trials.
This blood pressure effect becomes particularly dangerous if you’re already taking medication for high blood pressure or if you take certain other drugs that interact with tizanidine (more on that below). The drop tends to hit hardest in the hours after a dose, and some people experience a rebound rise in blood pressure later as the drug wears off. If you feel dizzy or lightheaded when standing, sitting up slowly and staying hydrated can help, but it’s a signal worth paying attention to.
Effects on the Liver
Tizanidine can stress the liver. In clinical trials, 6% of patients taking the drug showed abnormal liver enzyme levels, compared to 2% on placebo. Most of the time these elevations are mild and reversible, but in rare cases tizanidine can cause more significant liver injury, especially in people who already have some degree of liver impairment.
Because of this risk, liver enzyme levels are typically checked before starting tizanidine and again about one month after reaching the target dose. If you develop unexplained nausea, unusual fatigue, dark urine, or yellowing of the skin or eyes while taking tizanidine, those are signs your liver may not be handling the drug well.
Hallucinations and Psychotic Symptoms
This one surprises most people. In two controlled clinical studies, about 3% of patients (5 out of 170) experienced formed visual hallucinations or delusions while taking tizanidine. “Formed” means these weren’t vague visual disturbances; patients saw distinct images or scenes that weren’t there. Most of them recognized the hallucinations weren’t real, but one patient developed full psychosis. Another continued experiencing problems for at least two weeks after stopping the drug.
Three percent may sound low, but it’s high enough to be aware of, particularly if you live alone or are caring for someone taking this medication. If hallucinations develop, they’re a reason to stop the drug rather than push through.
Dangerous Drug Interactions
Tizanidine is broken down in the body by a specific liver enzyme called CYP1A2. Drugs that block this enzyme can cause tizanidine to build up to dangerously high levels in the blood, amplifying every side effect dramatically.
Two drugs are outright contraindicated with tizanidine: the antibiotic ciprofloxacin and the antidepressant fluvoxamine. In a study of healthy volunteers, ciprofloxacin increased peak blood levels of tizanidine 7-fold and overall drug exposure 10-fold. Fluvoxamine was even more extreme, increasing peak levels 12-fold and total exposure 33-fold. At those concentrations, participants experienced significant drops in blood pressure, excessive drowsiness, and impaired coordination. Taking a normal dose of tizanidine with either of these drugs is essentially like taking many times your prescribed amount.
Several other medications also slow tizanidine’s breakdown, though less dramatically. These include other fluoroquinolone antibiotics, certain heart rhythm medications, the stomach acid reducers cimetidine and famotidine, oral contraceptives, the antiviral acyclovir, and the asthma drug zileuton. If you’re prescribed any new medication while taking tizanidine, it’s worth checking whether it affects this enzyme pathway.
Allergic Reactions
Rarely, tizanidine can trigger anaphylaxis, a severe allergic reaction. Reported symptoms include difficulty breathing, hives, and swelling of the throat and tongue. This is uncommon but requires immediate emergency care if it occurs.
Why Side Effects Vary So Much
People’s experiences with tizanidine side effects vary widely, and a big reason is how the drug is absorbed. Taking tizanidine with food versus on an empty stomach, or taking the tablet versus the capsule form, changes how much of the drug actually reaches your bloodstream. This means the same dose can feel very different depending on how and when you take it. Switching between the tablet and capsule, or changing whether you take it with meals, can unexpectedly make side effects stronger or weaker.
The drug also has a relatively short duration of action, which is why its effects peak quickly and then fade. This short window means side effects tend to cluster in the first couple of hours after a dose. It also means that if you do experience something unpleasant, it will typically pass faster than with longer-acting medications. But it also means the body goes through cycles of the drug ramping up and wearing off throughout the day, which can contribute to the blood pressure fluctuations some people notice.
Higher doses predictably bring more side effects. Because side effects scale with the amount of drug in your system, many people find that the lowest dose that controls their muscle tightness is also the one with the most manageable side effect profile.