Can I take Mucinex DM and DayQuil together?

What is in Mucinex DM and DayQuil?

The fastest way to see the problem is to put the 2 Drug Facts labels side by side. Here is what each label lists as active ingredients.

Both lists include dextromethorphan HBr. That is the overlap. Guaifenesin, acetaminophen and phenylephrine each appear in only 1 of the 2 products. Other Mucinex DM strengths also contain dextromethorphan, so the same rule applies to them.

• Mucinex DM (12-hour tablet): guaifenesin 600 mg (expectorant, loosens mucus) and dextromethorphan HBr 30 mg (cough suppressant)
• DayQuil Cold and Flu LiquiCaps: acetaminophen 325 mg (pain and fever, the same drug as Tylenol), dextromethorphan HBr 10 mg (cough suppressant) and phenylephrine HCl 5 mg (nasal decongestant) per LiquiCap
• Plain Mucinex (12-hour tablet): guaifenesin 600 mg only

Why is doubling dextromethorphan a problem?

Each label sets its own daily limit for that product. Mucinex DM allows up to 4 tablets in 24 hours, which is 120 mg of dextromethorphan. DayQuil LiquiCaps allow up to 8 in 24 hours, which is 80 mg. Take both at full dose and you are at 200 mg in a day, well past what either label allows on its own.

MedlinePlus says to check cough and cold labels carefully before using 2 or more products at the same time, because they may contain the same active ingredient and taking them together could cause an overdose. It lists overdose symptoms such as nausea, vomiting, drowsiness, dizziness, unsteadiness, vision changes, a fast heartbeat, trouble breathing, hallucinations and seizures. MedlinePlus also says large amounts of dextromethorphan can cause serious side effects or death.

We can't give you a safe cutoff for stacking the 2 products, and neither label gives one. The safe plan is to stay inside 1 product's limit.

What can I take instead?

Pick based on your symptoms, and make sure only 1 product in your plan has dextromethorphan.

• Plain Mucinex + DayQuil: guaifenesin for chest mucus, plus DayQuil for fever, aches, cough and stuffy nose. No ingredient appears twice. Follow each label's own dosing.
• Mucinex DM alone: if your main problems are cough and chest mucus, with no fever or stuffy nose, Mucinex DM already covers the cough suppressant and the expectorant.
• Mucinex DM + plain acetaminophen (Tylenol): if you also need fever or pain relief, Mucinex DM has no acetaminophen, so a plain acetaminophen product doesn't overlap. Don't add DayQuil on top, because DayQuil has acetaminophen too.
• Check other boxes in your cabinet: many cough and cold products contain dextromethorphan, including "DM" products like Robitussin Cough and Chest DM and Tussin DM, and combos like Tylenol Cold and Cough. Read the active ingredients on every box before you add it.

I already took Mucinex DM. When can I take DayQuil?

Mucinex DM is an extended-release tablet labeled "12 hour", and its label doses it every 12 hours. No label says exactly how long to wait before switching to DayQuil, so the cautious approach is to treat that tablet as covering you until your next dose would be due, 12 hours later. In that window, don't take DayQuil or any other product that has dextromethorphan.

If you need relief for fever or aches during those 12 hours, a plain acetaminophen product is an option, as long as you are not taking anything else with acetaminophen. The DayQuil label says severe liver damage may occur if you take more than 8 LiquiCaps in 24 hours or take it with other acetaminophen products.

Going the other way, DayQuil LiquiCaps are dosed every 4 hours. If you took DayQuil and want a mucus loosener, plain Mucinex fits. Mucinex DM does not.

Who should check with a doctor or pharmacist first?

Some warnings on these labels matter even if you take only 1 product. A pharmacist can check your list for you.

• MAOI antidepressants: both labels say do not use if you take a prescription MAOI, or within 2 weeks of stopping one. If you are not sure whether a medicine is an MAOI, ask a doctor or pharmacist first.
• High blood pressure or heart disease: DayQuil contains phenylephrine, a decongestant, and its label says to ask a doctor first if you have high blood pressure, heart disease, thyroid disease, diabetes or trouble urinating from an enlarged prostate.
• Liver disease, 3 or more drinks a day, or warfarin: the DayQuil label says to ask first. Its liver warning, which covers drinking, is there because DayQuil contains acetaminophen.
• Long-lasting cough: both labels say ask a doctor first if you have a persistent or chronic cough, such as from smoking, asthma or emphysema, or a cough with a lot of mucus.
• Kids under 12, pregnancy or breastfeeding: Mucinex DM is not for children under 12. DayQuil says ask a doctor for ages 4 to under 12 and do not use under 4. Both labels say to ask a health professional before use if you are pregnant or breastfeeding.