What is the recommended dosing of Robitussin DM (dextromethorphan 5 mg/guaifenesin 100 mg) for adults and children aged 12 years and older?

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Last updated: June 14, 2026 • View editorial policy

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Robitussin DM Dosing Recommendation

For adults and children 12 years and older, the recommended dose of Robitussin DM (dextromethorphan 5mg/guaifenesin 100mg per mL) is 10-20 mL (2-4 teaspoonfuls) every 4 hours, not exceeding 6 doses in 24 hours. 1, 2

Dosing by Age Group

Adults and Children ≥12 Years

  • Dose: 10-20 mL (2-4 teaspoonfuls) every 4 hours
  • Maximum: 6 doses per 24 hours
  • This provides 50-100 mg dextromethorphan and 1000-2000 mg guaifenesin per dose 1, 2

Children 6 to <12 Years

  • Dose: 5-10 mL (1-2 teaspoonfuls) every 4 hours
  • Maximum: 6 doses per 24 hours 1, 2

Children <6 Years

  • Do not use 1, 2

Important Clinical Context

Dextromethorphan Component

The evidence shows that commonly recommended dextromethorphan dosages are likely subtherapeutic. Maximum cough reflex suppression occurs at 60 mg with prolonged effect 3. The standard Robitussin DM dose provides only 50-100 mg dextromethorphan per dose, which falls below the optimal therapeutic threshold identified in clinical studies.

However, antitussive agents show only small/weak benefit for acute bronchitis and have mixed results in clinical trials 4. The ACCP guidelines rate antitussives as Grade C recommendation (fair evidence, small/weak benefit) 4.

Guaifenesin Component

Mucokinetic agents (expectorants like guaifenesin) are not recommended for acute bronchitis due to conflicting evidence and no consistent favorable effect on cough 4. The ACCP gives this a Grade I recommendation (fair evidence, conflicting benefit) 4.

Critical Caveats

  • Acute viral cough is almost invariably benign and prescribed treatment can be regarded as unnecessary 3
  • Simple home remedies like honey and lemon may be equally effective 3
  • Care must be taken with combination preparations containing other ingredients like acetaminophen when considering higher doses 3
  • The placebo effect is substantial in cough studies, making true efficacy difficult to establish 5, 6

When NOT to Use

  • Children under 6 years of age
  • When seeking to increase cough clearance in bronchitis (guaifenesin not effective for this) 4
  • As first-line therapy when simple supportive measures haven't been tried

References

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.