Does Chlorzoxazone Cause Dry Mouth?
No, chlorzoxazone does not cause dry mouth (xerostomia) based on the FDA-approved prescribing information, which does not list this as a known adverse effect. 1
Evidence from FDA Drug Labeling
The official FDA prescribing information for chlorzoxazone lists the following adverse reactions: 1
- Gastrointestinal effects: Possible gastrointestinal bleeding (rare instances)
- Central nervous system effects: Drowsiness, dizziness, light-headedness, malaise, or overstimulation (occasional)
- Dermatologic reactions: Allergic-type skin rashes, petechiae, or ecchymoses (rare)
- Severe allergic reactions: Angioneurotic edema or anaphylactic reactions (extremely rare)
- Urine discoloration: Rarely noted, resulting from a phenolic metabolite (no clinical significance)
Notably absent from this comprehensive list of adverse reactions is any mention of dry mouth or xerostomia. 1
Mechanism Considerations
Chlorzoxazone is a centrally acting muscle relaxant that does not have significant anticholinergic properties, which are the primary mechanism by which most medications cause dry mouth. 2, 3 Unlike other muscle relaxants such as cyclobenzaprine (which has significant anticholinergic effects and commonly causes dry mouth), chlorzoxazone works through different mechanisms that do not typically affect salivary gland function. 2
Clinical Context
While many medications commonly cause xerostomia—including anticholinergics, tricyclic antidepressants, opioids, and certain muscle relaxants like cyclobenzaprine—chlorzoxazone is not among the documented xerogenic agents. 2, 4, 3 If a patient taking chlorzoxazone reports dry mouth, consider alternative causes such as:
- Concomitant medications with known xerogenic effects 4, 3
- Dehydration from inadequate fluid intake 5
- Underlying conditions such as Sjögren's syndrome 2
- Other medications the patient may be taking concurrently 6
Important Safety Considerations
While dry mouth is not a concern with chlorzoxazone, clinicians should be aware of its serious potential adverse effects, particularly rare but potentially fatal hepatocellular toxicity. 1 Patients should be instructed to report early signs of hepatotoxicity including fever, rash, anorexia, nausea, vomiting, fatigue, right upper quadrant pain, dark urine, or jaundice, and the medication should be discontinued immediately if these develop. 1