Dextromethorphan Side Effects: What to Know

Overview

Dextromethorphan is generally well-tolerated when used as directed at recommended doses for temporary cough suppression. Most people experience few or no side effects, and when side effects do occur, they are typically mild. However, misuse of dextromethorphan at doses significantly exceeding recommendations can cause serious adverse effects. Understanding the potential side effects, their frequency, and when they warrant medical attention can help people use dextromethorphan safely and know when to seek guidance from a healthcare provider.

This page provides detailed information about dextromethorphan’s side effects, organized by frequency and severity, along with information about risk factors, interaction-related effects, and when to seek medical care.

Common Side Effects

Side effects from dextromethorphan at recommended doses are generally uncommon and mild when they occur.

Drowsiness or Dizziness

Mild drowsiness or dizziness is the most commonly reported side effect of dextromethorphan, occurring in a small percentage of people. This effect is generally mild and may be more noticeable when first starting the medication.

Managing drowsiness or dizziness:

Avoid driving or operating machinery if affected
Avoid alcohol, which can worsen drowsiness
Do not combine with other medications that cause drowsiness without healthcare provider guidance
Take at bedtime if using for nighttime cough control

The drowsiness effect can actually be beneficial for people whose cough interferes with sleep.

Nausea or Upset Stomach

Some people experience mild nausea or stomach discomfort while taking dextromethorphan. This is generally mild and often resolves on its own.

Managing nausea or upset stomach:

Take with food if stomach upset occurs
Drink plenty of fluids
Avoid taking on an empty stomach if this seems to worsen nausea

If nausea is severe or persistent, medical evaluation may be appropriate.

Mild Stomach Pain

Mild abdominal discomfort can occur in some people taking dextromethorphan. This is generally temporary and not a cause for concern unless it becomes severe.

Constipation

Constipation may occur in some people, particularly with regular use. This is generally mild and can often be managed with dietary changes and adequate fluid intake.

Less Common Side Effects

Some side effects occur less frequently but are still reported by people taking dextromethorphan at recommended doses.

Confusion or Difficulty Concentrating

Some people report mild confusion, difficulty focusing, or a feeling of mental fogginess while taking dextromethorphan. This is generally mild at recommended doses but becomes more pronounced at higher doses.

Headache

Headache occurs in some people taking dextromethorphan, though it is relatively uncommon. Headaches are generally mild and often resolve on their own.

Nervousness or Restlessness

Some people, particularly children, may experience nervousness, restlessness, or agitation while taking dextromethorphan. This paradoxical stimulant effect is uncommon but recognized.

Fatigue

Some individuals experience increased tiredness or fatigue beyond mild drowsiness. This is generally temporary.

Other Less Common Effects

Additional less common side effects may include:

Dry mouth
Mild skin rash or itching
Sweating
Blurred vision
Mild tremor
Sleep disturbances or vivid dreams

Rare but Serious Side Effects

Serious side effects from dextromethorphan are rare at recommended doses, but they require prompt medical attention when they occur.

Severe Allergic Reactions

Although uncommon, some people can have an allergic reaction to dextromethorphan itself.

Signs of a severe allergic reaction may include:

Difficulty breathing or wheezing
Swelling of the face, lips, tongue, or throat
Severe rash, hives, or itching
Tightness in the chest
Rapid heartbeat
Severe dizziness or fainting

These symptoms require emergency medical attention. Anaphylaxis (a severe, life-threatening allergic reaction) is extremely rare but possible.

Serotonin Syndrome

When dextromethorphan is combined with certain medications that affect serotonin levels (particularly MAOIs, but also SSRIs and other antidepressants), a dangerous condition called serotonin syndrome can occur.

Signs of serotonin syndrome may include:

Severe confusion or agitation
Hallucinations
Rapid heart rate
High blood pressure
Fever
Excessive sweating
Muscle rigidity or twitching
Loss of coordination
Severe nausea or vomiting
Diarrhea
Seizures

Serotonin syndrome is a medical emergency requiring immediate treatment. The risk is highest when dextromethorphan is combined with MAOIs, which is why this combination is contraindicated.

Hallucinations or Severe Confusion

At recommended doses, hallucinations and severe confusion are extremely rare. However, at doses significantly exceeding recommendations, dextromethorphan can cause dissociative effects, hallucinations, and severe mental status changes.

Rapid or Irregular Heartbeat

Abnormal heart rhythms or palpitations are rare but have been reported, particularly at higher doses or when combined with other medications affecting heart rhythm.

Breathing Problems

While dextromethorphan is used to suppress cough, serious breathing difficulties or respiratory depression are rare but have been reported, particularly in people with underlying respiratory conditions or when combined with other central nervous system depressants.

Effects of Misuse and Overdose

Dextromethorphan is sometimes intentionally misused, particularly by adolescents, for its dissociative and hallucinogenic effects at very high doses (significantly exceeding recommended amounts).

Effects of Intentional Misuse

At doses far exceeding recommendations (often 5 to 10 times the recommended dose or more), dextromethorphan can cause:

Severe hallucinations (visual and auditory)
Dissociation (feeling detached from reality or one’s body)
Extreme confusion or disorientation
Slurred speech
Severe lack of coordination
Rapid or irregular heartbeat
High blood pressure
Severe nausea and vomiting
Muscle rigidity or involuntary movements
Loss of consciousness
Seizures
Respiratory depression
Potentially life-threatening complications

Important safety note:

Intentional misuse of dextromethorphan is dangerous and can be fatal. The dissociative effects sought by individuals misusing the medication come with significant risks of serious harm.

Signs of Overdose

Signs that someone may have taken too much dextromethorphan include:

Extreme drowsiness or inability to stay awake
Severe confusion or inability to respond appropriately
Hallucinations
Rapid heart rate
Dilated pupils
Muscle twitching or rigidity
Loss of coordination or ability to walk
Slurred speech
Nausea and vomiting
Breathing difficulties
Loss of consciousness
Seizures

Overdose is a medical emergency requiring immediate attention.

Risk Factors for Side Effects

Certain factors may increase the likelihood or severity of side effects from dextromethorphan.

Children:

Not recommended for children under 4 years of age
Children 4 to 6 should use only under healthcare provider direction
May be more prone to side effects at given doses due to smaller body size
Risk of accidental overdose if dosing is not carefully measured

Adolescents:

Higher risk of intentional misuse seeking dissociative effects
Proper storage and supervision may be appropriate

Elderly individuals:

May be more sensitive to drowsiness, dizziness, and confusion
May have slower metabolism leading to higher drug levels
Should use lower doses and monitor for increased sensitivity

Liver Function

Dextromethorphan is metabolized in the liver. People with liver disease may metabolize it more slowly.

Considerations for liver disease:

Medication can accumulate to higher levels
Increased risk of side effects
May require lower doses
Healthcare provider guidance is essential

Genetic Variations in Metabolism

Some people have genetic variations in liver enzymes that metabolize dextromethorphan (specifically CYP2D6 enzyme). These individuals may be “poor metabolizers” or “ultra-rapid metabolizers.”

Poor metabolizers:

Break down dextromethorphan more slowly
May experience increased effects and side effects at standard doses
Estimated 5 to 10% of the population

Ultra-rapid metabolizers:

Break down dextromethorphan more quickly
May experience reduced effectiveness at standard doses

Concurrent Medications

Medications that significantly interact include:

MAOIs (monoamine oxidase inhibitors): Contraindicated - can cause serotonin syndrome
SSRIs and other antidepressants: Increased risk of serotonin syndrome
Medications that inhibit liver enzymes (quinidine, fluoxetine, bupropion, paroxetine): Can increase dextromethorphan levels
Other CNS depressants (sedatives, alcohol, opioids): Additive drowsiness and respiratory depression risk

Multiple Product Use

Taking multiple cough, cold, and flu products simultaneously can result in excessive dextromethorphan intake if multiple products contain it as an ingredient.

Individual Sensitivity

Some people are simply more sensitive to the effects of medications, including dextromethorphan. This individual variation is normal and unpredictable.

Comparing Side Effects with Other Cough Medications

Dextromethorphan’s side effect profile differs from other types of cough medications.

Compared to guaifenesin (expectorant):

Guaifenesin is generally even better tolerated with fewer side effects
Guaifenesin does not cause drowsiness or CNS effects
Dextromethorphan has more potential for CNS side effects (drowsiness, dizziness, confusion)
Neither has significant abuse potential at recommended doses, but dextromethorphan has higher abuse potential at excessive doses

Compared to codeine (prescription cough suppressant):

Codeine is a narcotic opioid with significant abuse and addiction potential
Codeine causes more constipation and drowsiness
Codeine has respiratory depression risk at therapeutic doses
Dextromethorphan at recommended doses has lower abuse potential

Compared to antihistamines (when used for cough):

Antihistamines like diphenhydramine tend to be more sedating
Both can cause drowsiness and dry mouth
Antihistamines may cause more anticholinergic effects (urinary retention, constipation)

For detailed comparisons, see our dextromethorphan vs guaifenesin comparison page.

Drug Interactions Leading to Side Effects

MAOI Interaction

The most serious interaction is with MAOIs. Combining dextromethorphan with MAOIs can cause serotonin syndrome, a potentially life-threatening condition. This combination is contraindicated.

MAOIs include medications such as:

Phenelzine (Nardil)
Tranylcypromine (Parnate)
Isocarboxazid (Marplan)
Selegiline (at higher doses)

Do not use dextromethorphan if taking an MAOI or within 14 days of stopping an MAOI.

SSRI and Antidepressant Interactions

While less dangerous than the MAOI interaction, combining dextromethorphan with SSRIs or other antidepressants can increase the risk of serotonin syndrome, particularly at higher doses.

Examples include:

Fluoxetine (Prozac)
Paroxetine (Paxil)
Sertraline (Zoloft)
Bupropion (Wellbutrin)
Many others

People taking antidepressants should consult a healthcare provider or pharmacist before using dextromethorphan.

Medications That Increase Dextromethorphan Levels

Some medications inhibit the liver enzymes that break down dextromethorphan, potentially leading to higher levels and increased side effects.

Examples include:

Quinidine
Fluoxetine
Paroxetine
Bupropion
Certain antifungals

Managing Minor Side Effects

For people who experience mild side effects but need to continue using dextromethorphan for cough control, several strategies may help:

For drowsiness:

Take at bedtime if possible
Avoid driving or operating machinery
Avoid alcohol and other sedating medications
Consider whether drowsiness is actually beneficial for sleep disrupted by cough

For nausea or upset stomach:

Take with food
Drink plenty of fluids
Try a different formulation if possible

For mild confusion or difficulty concentrating:

Avoid tasks requiring full mental clarity
Consider whether cough severity justifies continued use
Consult healthcare provider if concerning

If side effects persist, worsen, or interfere with daily activities, consulting a healthcare provider is advisable.

When to Contact a Healthcare Provider

Medical guidance should be sought in certain situations related to side effects.

Contact a healthcare provider if:

Side effects persist or worsen over time
New or unusual symptoms develop after starting dextromethorphan
There is uncertainty about whether a symptom is related to the medication
Side effects significantly interfere with daily activities
Questions arise about interactions with other medications being taken
Cough persists beyond 7 days despite medication use
Considering dextromethorphan use while taking antidepressants or other prescription medications

When to Seek Emergency Care

Some symptoms require immediate medical attention.

Seek emergency medical care if:

Difficulty breathing, severe wheezing, or chest tightness occurs
Severe swelling of the face, lips, tongue, or throat develops
Signs of anaphylaxis appear (severe rash, rapid pulse, dizziness, severe difficulty breathing)
Signs of serotonin syndrome develop (severe confusion, hallucinations, rapid heart rate, muscle rigidity, fever)
Hallucinations or severe confusion occur
Rapid or irregular heartbeat occurs
Seizures occur
Loss of consciousness
Signs of overdose appear (especially in cases of suspected intentional misuse)
Coughing up blood

These symptoms may indicate serious adverse reactions or other medical emergencies requiring immediate evaluation.

Important Safety Reminders

Use Only as Directed

Taking more than the recommended dose significantly increases the risk of side effects and potentially dangerous reactions. Never exceed recommended doses.

Check for Drug Interactions

Always inform healthcare providers about dextromethorphan use, especially if taking antidepressants, MAOIs, or other prescription medications.

Avoid Duplicate Dosing

Many cold and flu products contain dextromethorphan. Check all medication labels to avoid taking multiple products containing the same ingredient.

Secure Storage

Store dextromethorphan securely to prevent accidental ingestion by children and to reduce the risk of intentional misuse by adolescents.

Duration Limit

Do not use for more than 7 days without medical evaluation. Persistent cough may indicate a condition requiring different treatment.

Sources

This information is based on data from the following authoritative sources:

U.S. Food and Drug Administration (FDA). Dextromethorphan Label Information.
MedlinePlus, U.S. National Library of Medicine. Dextromethorphan.
National Institutes of Health (NIH). Dextromethorphan—Adverse Effects Profile.
FDA Consumer Health Information. Cough and Cold Medicine Safety.
FDA Adverse Event Reporting System (FAERS). Dextromethorphan Safety Data.
Clinical Toxicology. Dextromethorphan Abuse and Toxicity.
Journal of Clinical Pharmacology. Antitussive Safety and Tolerability.