[5] Serious side effects may include low blood pressure, liver problems, psychosis, and QT prolongation.

[4] Side effects include dizziness, drowsiness, weakness, nervousness, confusion, hallucinations, strange dreams, depression, vomiting, dry mouth, constipation, diarrhea, stomach pain, heartburn, increased muscle spasms, back pain, rash, sweating, and a tingling sensation in the arms, legs, hands, and feet.

[9] Symptoms of overdose in 45 cases reported to a poison control center included: lethargy, bradycardia, hypotension, agitation, confusion, vomiting and coma.

[10] Concomitant use of tizanidine and moderate or potent CYP1A2 inhibitors (such as zileuton, certain antiarrhythmics (amiodarone, mexiletine, propafenone, verapamil), cimetidine, famotidine, aciclovir, ticlopidine and oral contraceptives) is contraindicated.

Fluoroquinolone antibiotics such as moxifloxacin, levofloxacin, and ciprofloxacin should also be avoided due to an increased serum concentration of tizanidine when administered concomitantly.

The amine intermediate was treated with benzoyl chloride and ammonium thiocyanate followed by alkaline hydrolysis to form a thiourea.