Robitussin (Guaifenesin) Dosing for Adults
For adults, the recommended dose of guaifenesin (Robitussin) is 10 to 20 mL (200-400 mg) every 4 hours, not exceeding 6 doses in 24 hours. 1
Standard Dosing Regimen
Immediate-Release Formulation:
- Dose: 10 to 20 mL (2 to 4 teaspoonfuls) every 4 hours 1
- Maximum frequency: Do not exceed 6 doses in any 24-hour period 1
- Timing: Multiple daily doses are needed to maintain therapeutic effect throughout the day due to guaifenesin's short half-life 2
Extended-Release Formulation Alternative
Extended-Release Tablets (if available):
- Dose: 600-1200 mg every 12 hours 3
- Advantage: Provides convenience with twice-daily dosing instead of every 4 hours 3
- Bioequivalence: Extended-release formulations at 1200 mg every 12 hours are bioequivalent to 400 mg immediate-release every 4 hours 3
Administration Instructions
Key directions for optimal use:
- Take with a full glass of water to enhance the expectorant effect 2
- Can be taken with or without food, though food may delay time to peak concentration with extended-release formulations 3
- The flexible dosing range (200-400 mg per dose) allows titration based on symptom severity 2
Mechanism and Clinical Use
How guaifenesin works:
- Acts as an expectorant by loosening mucus in the airways and making coughs more productive 2
- The expectorant action is mediated through stimulation of the gastrointestinal tract, not systemic absorption 4
- Helps relieve wet cough and chest congestion associated with upper respiratory tract infections 2
Important Caveats
Limitations to be aware of:
- Guaifenesin is the only legally marketed expectorant in the US per OTC Monograph 2
- While it has FDA approval for helping loosen phlegm, objective evidence of antitussive (cough-suppressing) effect is limited 5
- Patients reported subjective improvement in sputum thickness (96% vs 54% placebo) and quantity (88% vs 62% placebo) in clinical studies 5
- The immediate-release liquid formulation requires frequent dosing every 4 hours to maintain 24-hour therapeutic effect 2