Dextromethorphan Dosage: Same 5 mL, 6 Times the Dose in Delsym 12-Hour

Quick Answer: There is no single dextromethorphan dose, because the products differ six-fold in strength per millilitre. Delsym 12-Hour liquid contains dextromethorphan polistirex “equivalent to 30 mg dextromethorphan hydrobromide” in each 5 mL, and its label says adults and children 12 and over take 10 mL every 12 hours, not to exceed 20 mL in 24 hours. Children’s Delsym Cough + Chest Congestion DM contains 5 mg in each 5 mL and is given every 4 hours. Immediate-release tablets and capsules (15 mg each) are labelled 2 every 6 to 8 hours, not more than 8 in 24 hours, for ages 12 and over. Every label we read says do not use with a prescription MAOI antidepressant or within 2 weeks of stopping one, and the children’s liquids say do not use under 4 years. Measure only with the cup that came in the box. On whether it works: a Cochrane review of 29 trials found “no good evidence for or against” over-the-counter cough medicines. We do not link to any product on this page.

Dextromethorphan (DXM, the “DM” on cough syrup boxes) is the cough suppressant in Delsym, Robitussin DM, many store brands, and most DayQuil and NyQuil products. The dose question people search for usually has the same problem as the other medicines in our Sudafed PE and adult Tylenol pages: the brand name does not tell you the dose, the box does. This page copies the directions from six current Drug Facts labels on DailyMed, the National Library of Medicine’s label database, and then sets out what the trials and the FDA say.

Dextromethorphan dosage by product, from the labels

Every dose and limit in this table is quoted or copied from the label named in the first column. Where we give a milligram total that the label does not print, it is our multiplication of the label’s own figures, and we say so.

Read across the rows and the point of the title appears. A 5 mL dose of Delsym 12-Hour carries dextromethorphan equivalent to 30 mg of the hydrobromide; 5 mL of either children’s DM syrup carries 5 mg. The same spoonful is six times the drug, and the two are meant to be given on different clocks: every 12 hours for the extended-release suspension, every 4 hours for the immediate-release syrups. Swapping the cup from one box to the other, or assuming “cough syrup is cough syrup”, is how the dose goes wrong. The Delsym label says it directly: “measure only with dosing cup provided” and “do not use dosing cup with other products”.

The daily totals behind the limits

These are our multiplication of the label figures, not numbers printed on the boxes. Two 15 mg caplets is 30 mg a dose, and the 8-caplet limit works out to 120 mg in 24 hours. Robitussin Maximum Strength’s 20 mL is 20 mg a dose, and six doses is 120 mg. Delsym 12-Hour’s 20 mL limit is four 5 mL measures of the 30 mg equivalent, which is also 120 mg. The adult limits converge on the same daily total; it is the size and timing of each dose that differs.

Who should not take it, from the labels

Every label we read carries the same first warning:

“Do not use if you are now taking a prescription monoamine oxidase inhibitor (MAOI) (certain drugs for depression, psychiatric, or emotional conditions, or Parkinson’s disease), or for 2 weeks after stopping the MAOI drug.”

If you are not sure whether a prescription is an MAOI, the labels say to ask a doctor or pharmacist before taking the product. The Delsym 12-Hour label then lists when to ask a doctor first: “chronic cough that lasts such as occurs with smoking, asthma, or emphysema” and “cough that occurs with too much phlegm (mucus)”. It tells you to stop and ask a doctor “if cough lasts more than 7 days, comes back, or occurs with fever, rash, or headache that lasts”, adding: “These could be signs of a serious condition.” Pregnant or breastfeeding readers are told to ask a health professional before use.

Children: what the labels and the FDA say

All three children’s labels in our table say “do not use” under 4 years. That line comes from a 2008 change. The FDA’s consumer page explains that manufacturers “voluntarily removed over-the-counter (OTC) infant cough and cold products intended for children under 2 years of age due to these safety concerns”, and that products for older children were “voluntarily re-labeled” to state “do not use in children under 4 years of age.”

The FDA page gives the reason: “During 2004-2005, an estimated 1,519 children less than 2 years of age were treated in U.S. emergency departments for adverse events, including overdoses, associated with cough and cold medications.” For children 4 and over it warns that these products “can be harmful if” more than the recommended amount is used, they are given too often, or “more than one product containing the same drug is being used”, and that “Children should not be given medicines that are packaged and made for adults.”

The last warning matters for dextromethorphan in particular, because it is in so many combination products. A child given a DM cough syrup and a multi-symptom cold liquid may be getting dextromethorphan from both. The children’s labels in our table are dosed by age, not weight, and give a range for some ages; the FDA’s advice is to read the Drug Facts label for each product rather than to assume.

Does dextromethorphan work?

This is where the evidence is thinner than the shelf space suggests.

Adults and children: the Cochrane review

A 2014 Cochrane review of over-the-counter medicines for acute cough included “29 trials (19 in adults, 10 in children) involving 4835 people”. In adults, “six trials compared antitussives with placebo and had variable results.” In children, “antitussives (data from three studies)” were “no more effective than placebo”. The authors judged the trials too different to pool and concluded: “There is no good evidence for or against the effectiveness of OTC medicines in acute cough.” They also noted “higher numbers of adverse effects in participants taking preparations containing antihistamines and dextromethorphan.”

Two trials in children at night

Two randomized trials led by the same first author tested dextromethorphan for night-time cough in children with colds.

• Dextromethorphan vs diphenhydramine vs placebo (2004). Parents of 100 children with upper respiratory infections reported on night cough and sleep. Everyone improved on the second night, “However, neither diphenhydramine nor dextromethorphan produced a superior benefit when compared with placebo for any of the outcomes studied.” Insomnia “was reported more frequently in those who were given dextromethorphan”.
• Honey vs dextromethorphan vs no treatment (2007). 105 children aged 2 to 18 received a single dose of buckwheat honey, honey-flavoured dextromethorphan, or nothing before bed. Honey “was significantly superior to no treatment for cough frequency and the combined score, but DM was not better than no treatment for any outcome.” Honey and dextromethorphan did not differ significantly from each other. The trial enrolled children aged 2 and over, so it says nothing about younger children.

None of this shows that dextromethorphan never helps anyone. It shows that the trials have not demonstrated a clear benefit over placebo, which is a reasonable thing to know before giving it to a child, or before reaching for the strongest box on the shelf.

The combination-product problem

Search DailyMed for dextromethorphan and most of the results are not cough syrups at all. They are multi-symptom products: DayQuil and NyQuil liquids and capsules, store-brand “cold and flu” combinations, and nighttime cough formulas. Many add acetaminophen, an antihistamine such as doxylamine, or phenylephrine. The FDA’s warning about “more than one product containing the same drug” applies to adults too.

Two practical consequences. First, if you are already taking a cold-and-flu product with “DM” or dextromethorphan in the active ingredients, a separate cough syrup can double the dose. Second, the acetaminophen in many of these products counts toward the daily acetaminophen limit; our adult Tylenol page sets out those limits from the labels.

How to read your own box

1. Find the active ingredient line. It states the amount “in each 5 mL”, “in each 20 mL” or “in each caplet”. Note the volume, because labels use different ones.
2. Check for “extended release” or “12 hour”. Delsym 12-Hour is dosed every 12 hours; immediate-release products every 4 to 8 hours.
3. Check the other active ingredients. Guaifenesin, acetaminophen, antihistamines or phenylephrine change who can take it and what else you should avoid.
4. Use the cup in that box. Not a kitchen spoon and not the cup from another product.
5. Check the MAOI line against every prescription you take.
6. For children, start from the age row. Under 4: the labels say do not use.

Frequently Asked Questions

What is the dextromethorphan dosage for adults?

It depends on the product. Immediate-release 15 mg caplets and softgels: 2 every 6 to 8 hours, not more than 8 in 24 hours. Delsym 12-Hour liquid: 10 mL every 12 hours, not more than 20 mL in 24 hours. Robitussin Maximum Strength DM liquid: 20 mL every 4 hours, not more than 6 doses in 24 hours.

How much Delsym should I take?

The Delsym 12-Hour label says adults and children 12 and over take 10 mL every 12 hours, not to exceed 20 mL in 24 hours; children 6 to under 12 take 5 mL every 12 hours; children 4 to under 6 take 2.5 mL every 12 hours; under 4, do not use. Measure only with the cup provided.

What is the Robitussin DM dosage?

Robitussin Maximum Strength Cough + Chest Congestion DM: 20 mL every 4 hours for adults and children 12 and over, not more than 6 doses in 24 hours. Children’s Robitussin Cough and Chest Congestion DM: 5 mL for ages 4 to under 6, 10 mL for ages 6 to under 12, 20 mL for 12 and over, every 4 hours, not more than 6 doses in 24 hours.

Can I take dextromethorphan with an antidepressant?

Not with a prescription MAOI, or within 2 weeks of stopping one; every label we read says do not use. For other antidepressants, the labels do not list them, so ask a pharmacist before combining.

Can children under 4 take dextromethorphan?

The children’s labels we read say do not use under 4 years. The FDA says products for older children were re-labelled to say “do not use in children under 4 years of age.”

Does dextromethorphan actually work?

A Cochrane review found “no good evidence for or against” over-the-counter cough medicines in acute cough. Two pediatric trials found dextromethorphan no better than placebo or no treatment for night cough.

Is 5 mL of Delsym the same as 5 mL of other cough syrup?

No. Delsym 12-Hour contains the equivalent of 30 mg of dextromethorphan hydrobromide per 5 mL; the children’s DM syrups we read contain 5 mg per 5 mL. Use the dose and cup for the product you have.

The Bottom Line

Dextromethorphan doses are set by the product, not the ingredient. The extended-release Delsym 12-Hour suspension is six times stronger per millilitre than the children’s DM syrups (30 mg vs 5 mg in each 5 mL, per their labels) and is given every 12 hours instead of every 4, so the same spoonful is not the same dose. Every label says not to use it with an MAOI, the children’s labels say not under 4, and the trials have not shown a clear benefit over placebo. If you use it, use one product at a time, with its own cup, and stop and see a doctor if the cough lasts more than 7 days. This article is general information, not medical advice.

Sources

1. DailyMed. Delsym 12 Hour Cough Relief (dextromethorphan) suspension, extended release, Reckitt Benckiser LLC, set ID e3e1d126-76c2-4776-8ce0-449625b7e6ba (published 11 Sep 2026). “Dextromethorphan polistirex equivalent to 30 mg dextromethorphan hydrobromide” in each 5 mL; “10 mL every 12 hours, not to exceed 20 mL in 24 hours”; 6 to under 12 “5 mL every 12 hours, not to exceed 10 mL”; 4 to under 6 “2.5 mL every 12 hours, not to exceed 5 mL”; under 4 “do not use”; “measure only with dosing cup provided”; MAOI, ask-a-doctor and stop-use warnings (“cough lasts more than 7 days”). dailymed.nlm.nih.gov. Checked 14 October 2026.
2. DailyMed. Delsym Cough (dextromethorphan hydrobromide) tablet, Reckitt Benckiser LLC, set ID a43d59f9-3a6c-4a7c-b98d-b86d6035f716 (published 29 May 2026). 15 mg per caplet; “take 2 caplets every 6 to 8 hours as needed, not to exceed 8 caplets in 24 hours”; under 12 “do not use”. dailymed.nlm.nih.gov. Checked 14 October 2026.
3. DailyMed. Dextromethorphan Hydrobromide Capsules, 15 mg, Softgel Healthcare Pvt Ltd, set ID 20f7c1a9-fc4d-1f51-e063-6394a90a8be3 (published 12 Oct 2026). “take 2 capsules every 6 to 8 hours, as needed”; “do not take more than 8 capsules in any 24-hour period”. dailymed.nlm.nih.gov. Checked 14 October 2026.
4. DailyMed. Robitussin Maximum Strength Cough + Chest Congestion DM (dextromethorphan HBr, guaifenesin) solution, Haleon, set ID f1d022dd-c2ca-497f-87d5-9ef3e20e8ea7 (published 17 Nov 2025). 20 mg dextromethorphan HBr and 400 mg guaifenesin in each 20 mL; “20 ml every 4 hours”; “do not take more than 6 doses in any 24-hour period”; under 12 “do not use”. dailymed.nlm.nih.gov. Checked 14 October 2026.
5. DailyMed. Children’s Robitussin Cough and Chest Congestion DM (dextromethorphan hydrobromide, guaifenesin) liquid, Haleon, set ID b9772292-9eb6-47cf-abb8-007c25478090 (published 18 Mar 2024). 5 mg and 100 mg in each 5 ml; under 4 “do not use”; 4 to under 6 “5 ml”, 6 to under 12 “10 ml”, 12 and over “20 ml”, every 4 hours; not more than 6 doses in 24 hours. dailymed.nlm.nih.gov. Checked 14 October 2026.
6. DailyMed. Children’s Delsym Cough + Chest Congestion DM (dextromethorphan HBr and guaifenesin) solution, Reckitt Benckiser LLC, set ID d26b5143-aa07-4114-a6ba-4f503aadd46f (published 28 May 2026). 5 mg and 100 mg in each 5 mL; 6 to under 12 “5 mL – 10 mL every 4 hours”; 4 to under 6 “2.5 mL – 5 mL every 4 hours”; under 4 “do not use”; “do not give more than 6 doses in any 24-hour period”. dailymed.nlm.nih.gov. Checked 14 October 2026.
7. U.S. Food and Drug Administration. Use Caution When Giving Cough and Cold Products to Kids. Voluntary removal of products for children under 2; re-labelling “do not use in children under 4 years of age”; “an estimated 1,519 children less than 2 years of age” treated in emergency departments in 2004-2005; harm if “more than one product containing the same drug is being used”. fda.gov. Checked 14 October 2026.
8. Smith SM, Schroeder K, Fahey T. Over-the-counter (OTC) medications for acute cough in children and adults in community settings. Cochrane Database Syst Rev, 2014. 29 trials, 4835 people; adult antitussive trials “had variable results”; in children antitussives “no more effective than placebo”; “There is no good evidence for or against the effectiveness of OTC medicines in acute cough.” PMID 25420096. Checked 14 October 2026.
9. Paul IM, Yoder KE, Crowell KR, et al. Effect of dextromethorphan, diphenhydramine, and placebo on nocturnal cough and sleep quality for coughing children and their parents. Pediatrics, 2004. 100 children; “neither diphenhydramine nor dextromethorphan produced a superior benefit when compared with placebo”; insomnia more frequent with dextromethorphan. PMID 15231978. Checked 14 October 2026.
10. Paul IM, Beiler J, McMonagle A, et al. Effect of honey, dextromethorphan, and no treatment on nocturnal cough and sleep quality for coughing children and their parents. Arch Pediatr Adolesc Med, 2007. 105 children aged 2 to 18; single dose before bed; “DM was not better than no treatment for any outcome”; honey vs DM not significantly different. PMID 18056558. Checked 14 October 2026.