Drug reference

Dextromethorphan

Antitussive · Analgesic

Also known as Dextromethorphan Hydrobromide, DXM

START

Confirm non-productive cough. Rule out productive cough requiring expectoration. Screen for serotonergic medications (MAOIs, SSRIs, SNRIs).

TYPICAL MAX

120 mg/day (OTC). Do not exceed.

STOP IF

Signs of serotonin syndrome, severe allergic reaction, cough >7 days or with fever/rash (evaluate underlying cause)

WATCH

Cough duration and character, signs of serotonin syndrome if on other serotonergic drugs, abuse potential

CDSCO approvedOTC (Over-The-Counter) for single-ingredient formulations, but some fixed-dose combinations may be Schedule H.Jan AushadhiATC R05DA09

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 30min · 15-30 min
PEAK: 2h · 2-2.5 h (IR)
t½: 4h · 3-6 h (parent); 3-4 h (dextrorphan)
DURATION: 6h · 3-6 h (IR); 12 h (ER)

EXCRETION

Renal (metabolites); hepatic CYP2D6/CYP3A4; dextrorphan active metabolite

route + CYP

INTERACTIONS

12 major

incl. contraindicated

PREGNANCY

FDA PLLR: Animal studies showed no teratogenicity. Limited human data. Generally considered safe for short-term use during pregnancy. Avoid prolonged use.

FDA category + note

Top interactionssee all 12 →

Mao InhibitorsContraindicatedDatabaseKimi deep-research + Cla
MoclobemideSevereTextbookG&G 14e · p466
CitalopramSevereDatabaseDDInter
DesvenlafaxineSevereDatabaseDDInter

Available in India

29 branded formulations and 540 fixed-dose combinations. Look up specific brands in the Drugs workspace.

Jan Aushadhi — generic available at GoI pharmacies

Mechanism

Dextromethorphan is a synthetic morphinan derivative and the d-isomer of levorphanol. Unlike opioid analgesics, it lacks mu-opioid receptor affinity at antitussive doses. Its cough-suppressant effect is mediated primarily through inhibition of NMDA (N-methyl-D-aspartate) glutamate receptors in the medullary cough center, reducing the sensitivity of cough receptors and elevating the threshold for cough initiation. It also has sigma-1 receptor agonist activity and inhibits serotonin reuptake (SERT). At high doses, it produces dissociative and hallucinogenic effects similar to ketamine and phencyclidine (PCP).

Indications

Temporary relief of cough due to minor throat and bronchial irritationCough associated with common cold or inhaled irritantsNot effective for cough due to smoking, asthma, or emphysemaNeuropathic pain (combination with quinidine — off-label, Nuedexta)Pseudobulbar affect (PBA) — combination with quinidine (Nuedexta)

Dosing

Adult: Immediate-release: 10-20 mg PO q4h OR 30 mg q6-8h (max 120 mg/day). Extended-release: 60 mg PO q12h (max 120 mg/day). Combination products: follow specific product labeling.
Pediatric: 4-6 years: 2.5-5 mg q4h (max 30 mg/day). 6-12 years: 5-10 mg q4h OR 15 mg q6-8h (max 60 mg/day). 12+ years: adult dosing.
Renal adjustment: No adjustment required.
Hepatic adjustment: Use caution in severe hepatic impairment; may accumulate.
Geriatric: No specific adjustment; use lowest effective dose.
Max dose: 120 mg/day (OTC); 240 mg/day (prescription, combination products)

Pharmacokinetics

Onset

Cough suppression within 15-30 minutes.

Peak effect

Oral IR: peak plasma at 2-2.5 hours. ER: peak at 3-6 hours.

Duration

IR: 3-6 hours. ER: 12 hours.

Half-life

~3-6 hours (parent); dextrorphan (active metabolite via CYP2D6): 3-4 hours.

Bioavailability

~11% (oral; significant first-pass metabolism via CYP2D6).

Protein binding

~60-70%.

Metabolism

Extensive hepatic via CYP2D6 (O-demethylation to dextrorphan — active metabolite responsible for most pharmacological effects) and CYP3A4 (N-demethylation to 3-methoxymorphinan — inactive). CYP2D6 poor metabolizers have reduced dextrorphan formation and less cough suppression.

Excretion

Renal: primarily as metabolites (glucuronide conjugates of dextrorphan and 3-hydroxymorphinan).

Contraindications

Hypersensitivity to dextromethorphan
MAOI use within 14 days (serotonin syndrome risk)
Concurrent use with SSRIs, SNRIs, TCAs, triptans, linezolid (serotonin syndrome risk — relative)
Children <4 years (FDA advisory — lack of efficacy and safety data)

Side effects

Common

Drowsiness, dizzinessNausea, vomitingStomach upsetConstipation

Serious

Serotonin syndrome (when combined with MAOIs, SSRIs, SNRIs, TCAs, triptans — hyperthermia, agitation, myoclonus, autonomic instability, coma)
Severe allergic reactions (anaphylaxis, angioedema)
Psychological dependence and abuse (at supratherapeutic doses — dissociative/hallucinogenic effects)
Respiratory depression (at very high doses or with CNS depressants)
Hypertension (with MAOIs)

Pregnancy & lactation

Pregnancy

FDA PLLR: Animal studies showed no teratogenicity. Limited human data. Generally considered safe for short-term use during pregnancy. Avoid prolonged use.

Lactation

Excreted in breast milk in low concentrations. Compatible with breastfeeding per AAP. Avoid high doses.

Drug interactions

Mao Inhibitors

Contraindicated

Database

MAOIs + dextromethorphan = serotonin syndrome and hypertensive crisis. MAOIs prevent serotonin breakdown; dextromethorphan inhibits serotonin reuptake and is a serotonin releaser.

Do NOT use within 14 days of MAOI discontinuation. This is an absolute contraindication.

Source: Kimi deep-research + Cla

Moclobemide

Severe

Textbook

Can cause serotonin syndrome.

Dextromethorphan must be avoided in patients taking MAO inhibitors.

Source: G&G 14e · p466

Citalopram

Severe

Database

Drug interaction classified as: synergy.