Poly-Hist DM
Poly-Hist DM liquid is a combination of three medications: dextromethorphan (a cough suppressant), phenylephrine (a decongestant), and thonzylamine (an antihistamine). Poly-Hist DM is available over the counter for adults and children ages 6 years and older. It's taken by mouth every 4 hours as needed to ease symptoms of allergies or the common cold, such as cough, runny nose, and congestion. Possible side effects include sleepiness, dizziness, and headache.
What is Poly-Hist DM?
What is Poly-Hist DM used for?
Short-term relief of symptoms from allergies or the common cold:
Runny nose
Sneezing
Itchy or watery eyes
Itching of the nose or throat
Cough from throat and lung irritation
Stuffy nose (nasal congestion)
How Poly-Hist DM works
Poly-Hist DM is a combination of three medications that work together to relieve symptoms caused by the common cold and allergies.
Dextromethorphan is a cough suppressant. It's thought to work in the brain to lessen your urge to cough.
Phenylephrine is a decongestant. It's thought to work by tightening the blood vessels in the nose to relieve sinus pressure.
Thonzylamine is an antihistamine. It blocks the effects of a natural substance in your body called histamine. This lessens inflammation (swelling) and relieves runny nose, itchy nose, and sneezing.
Drug Facts
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What are the side effects of Poly-Hist DM?
Common Side Effects
- Sleepiness
- Nervousness
- Dizziness
- Nausea
- Stomach discomfort
Other Side Effects
- Dry mouth
- Trouble urinating
- Trouble sleeping
Serious Side Effects
- Serotonin syndrome (too much serotonin): fast heart rate, sweating, muscle stiffness or spasms, high fever, confusion
- Accidentally taking too much: anxiety or other behavior changes, severe dizziness, poor balance or coordination, high blood pressure, fast heartbeat, trouble breathing
Source: DailyMed
Pros and cons of Poly-Hist DM
Pros
Can treat a wide range of common cold or allergy symptoms
Conveniently combines three medications in one product
Available over the counter
Available as a bubblegum-flavored liquid for better taste
Sugar, alcohol, dye, and gluten free
Cons
Only available as a liquid
Might need to take as often as every 4 hours to relieve symptoms
Harder to customize the dose since it's a fixed combination of three medications
Might not be the best choice for people over 65 years old
Might not be a good choice for people with glaucoma or for people with heart, breathing, or urinary problems
Pharmacist tips for Poly-Hist DM
Take Poly-Hist DM with or without food. If the medication upsets your stomach, taking it with food might help.
Always use a medication dose cup or an oral syringe to measure out your Poly-Hist DM dose. Never use household kitchen spoons because they might not be accurate and using them might cause you to take the wrong dose. Ask your pharmacist for a measuring device for the medication if the packaging doesn't come with one.
Poly-Hist DM can make you sleepy or dizzy during the day, which can affect your ability to focus, think, or react. Don't drive or do anything that requires a lot of attention until you know how the medication affects you. To prevent daytime sleepiness, taking the least amount of medication possible at night can help.
Poly-Hist DM usually makes adults sleepy. But it's possible for children to become overly excited or energetic. Stop Poly-Hist DM and speak to a pediatrician if this happens to your child.
Stop taking Poly-Hist DM and contact your primary care provider (PCP) if your symptoms worsen or last longer than a week after you start taking Poly-Hist DM. Also stop taking the medication and speak with your PCP if you start to have a fever, rash, or any other new symptoms. These might be signs of a more serious problem.
Stop taking Poly-Hist DM and call your PCP if you experience dizziness, nervousness, or trouble sleeping. These might be side effects from the phenylephrine or the other ingredients in Poly-Hist DM. Depending on how severe your symptoms are, your PCP might recommend a lower dose of Poly-Hist DM or other medications to relieve your symptoms.
Read the active ingredients list on all the medications you're taking. Many over-the-counter allergy, cough, cold, and flu medications contain similar or the same ingredients as those in Poly-Hist DM. Taking more than one cough suppressant, decongestant or antihistamine at the same time can raise the risk of dangerous side effects, like confusion and trouble breathing.
Don't take Poly-Hist DM within 2 weeks of a monoamine oxidase inhibitor (MAOI), like selegiline or phenelzine (Nardil). Poly-Hist DM interacts with these medications, which can raise your risk for a serious side effect called serotonin syndrome. Ask your PCP for other options to relieve your cold or allergy symptoms.
Frequently asked questions about Poly-Hist DM
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What are the risks and warnings for Poly-Hist DM?
Poly-Hist DM can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.
Serotonin syndrome
Risk factors: Taking monoamine oxidase inhibitors (MAOIs) 14 days before starting Poly-Hist DM | Taking other medications that raise serotonin levels in the brain
Poly-Hist DM contains dextromethorphan. Dextromethorphan can raise the serotonin levels in the brain and put you at risk for a rare but serious side effect called serotonin syndrome. Your risk is higher if you're also taking other medications that affect serotonin levels, such as certain antidepressants, MAOIs, and certain migraine medications.
Make sure your healthcare team knows about all the medications you take (including over-the-counter medications and supplements). They can check that Poly-Hist DM is safe for you to take with your other medications. Don't start any new medications while you're taking Poly-Hist DM without letting your pharmacist or primary care provider know.
Get medical help right away if you have any symptoms of serotonin syndrome, such as fast heart rate, sweating, muscle stiffness or spasms, high fever, and confusion.
Accidentally taking too much (overdose)
Poly-Hist DM contains a cough suppressant (dextromethorphan), a decongestant (phenylephrine), and an antihistamine (thonzylamine). Taking more than one medication containing an antihistamine, cough suppressant, or a decongestant can lead to an accidental overdose. An overdose can be life-threatening.
To prevent an accidental overdose, read the medication box and package labels carefully so you're aware of the ingredients, age-cut offs, and maximum dosing for your medications. Ask your primary care provider or pharmacist if you're not sure whether you're taking a medication that has the same or similar ingredients as Poly-Hist DM.
Some signs of taking too much medication can include anxiety or other behavior changes, severe dizziness, high blood pressure, and trouble breathing. If you or your loved one has signs or symptoms of an accidental overdose, get medical help as soon as possible.
Worsening of certain medical conditions
Risk factors: Heart disease | High blood pressure | Thyroid problems | High blood sugar (diabetes) | Glaucoma | Mucus-producing cough | Breathing problems (e.g., asthma, emphysema, long-term bronchitis) | Urinary conditions
Poly-Hist DM is generally safe to take, but it might not be the best choice for everyone depending on your medical conditions. Make sure your primary care provider and pharmacist know about all your health conditions before you take Poly-Hist DM. Ask them whether this medication is safe and appropriate for you.
If you're 65 years or older or taking other medications that can make you sleepy, you're at higher risk for side effects from thonzylamine, such as accidental falls. And if you have a cough that's lasted for a long time; a cough that occurs with smoking, asthma, or emphysema; or a cough with a lot of mucus, Poly-Hist DM might not be right for you. Poly-Hist DM can also worsen heart disease, high blood pressure, thyroid problems, diabetes, glaucoma, trouble urinating, or breathing problems. Speak with a healthcare professional about whether Poly-Hist DM is safe for you if you have any of these medical conditions.
Poly-Hist DM dosage forms
| Dosage | Quantity | Price as low as | Price per unit |
|---|---|---|---|
| 473ml of 10mg/5mg/25mg/5ml | 1 bottle | $83.33 | $83.33 |
Typical dosing for Poly-Hist DM
Each 5 mL of Poly-Hist DM contains 10 mg of dextromethorphan, 5 mg of phenylephrine, and 25 mg of thonzylamine.
Adults and children 12 years or older: The typical dose is 10 mL by mouth every 4 hours when you have symptoms. Don't take more than 6 doses (60 mL) in a 24-hour period.
Children age 6 years to under 12 years old: The typical dose is 5 mL by mouth every 4 hours when you have symptoms. Don't take more than 6 doses (30 mL) in a 24-hour period.
Children under 6 years old: Ask a healthcare professional or your child's primary care provider.
How much does Poly-Hist DM cost?
Poly-Hist DM contraindications
Currently taking or have taken a monoamine oxidase inhibitor (MAOI) in the last 14 days
What are alternatives to Poly-Hist DM?
Short-term relief of symptoms from allergies or the common cold:
Runny nose
Sneezing
Itchy or watery eyes
Itching of the nose or throat
Cough from throat and lung irritation
Stuffy nose (nasal congestion)
Cough from throat and lung irritation
Runny nose
Sneezing
Itchy or watery eyes
Itching of the nose or throat
Stuffy nose (nasal congestion)
Runny nose
Sneezing
Itchy nose or throat
Itchy, watery eyes
Cough from throat and lung irritation
Stuffy nose (nasal congestion)
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References
Best studies we foundBorowy, C. S., et al. (2023). Antihistamine toxicity. StatPearls.
DrugBank Online. (2025). Thonzylamine.
Gelotte, C. K., et al. (2015). Pharmacokinetics, safety and cardiovascular tolerability of phenylephrine HCl 10, 20, and 30 mg after a single oral administration in healthy volunteers. Clinical Drug Investigation.
Poly Pharmaceuticals, Inc. (2024). Poly-Hist DM- dextromethorphan hydrobromide, phenylephrine hcl and thonzylamine hcl liquid [package insert]. DailyMed.
Preuss, C. V., et al. (2023). Prescription of controlled substances: Benefits and risks. StatPearls.
Schwartz, A. R., et al. (2008). Dextromethorphan-induced serotonin syndrome. Clinical Toxicology.
Talbert, M. et al. (2018). How much do oral decongestants increase blood pressure in patients with hypertension? Evidence-Based Practice.
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