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Poly-Hist DM

dextromethorphan / phenylephrine / thonzylamine
Used for Allergic Rhinitis, Cold Symptoms, Cough, Nasal Congestion

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.

Reviewed by:Last reviewed on January 2, 2025
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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

Common BrandsPoly-Hist DM
Drug ClassCough suppressant / Decongestant / Antihistamine
Controlled Substance ClassificationNot a controlled medication
Generic StatusNo lower-cost generic available
AvailabilityOver-the-counter
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Side effects of Poly-Hist DM

The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.

Common Side Effects

Less Common Side Effects

Poly-Hist DM serious side effects

Contact your healthcare provider immediately if you experience any of the following.

  • 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

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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
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Pharmacist tips for Poly-Hist DM

pharmacist
  • 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.
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Common questions about Poly-Hist DM

You might notice certain symptoms improving within 30 minutes after you take Poly-Hist DM. But the effects of the medication don't typically last long, so you might need to take the medication as often as every 4 hours to control your symptoms.

No. Poly-Hist DM isn't considered a narcotic. Narcotics refer to opioid medications. Poly-Hist DM doesn't have an opioid in it, so it isn't a narcotic.

It's possible. Phenylephrine, one of the active ingredients in Poly-Hist DM, can potentially raise your blood pressure. But it isn't very likely. If you already have high blood pressure or if you're taking other medications that can raise blood pressure though, you might be more likely to have higher blood pressure while you're taking Poly-Hist DM. Ask a member of your healthcare team whether Poly-Hist DM is safe for you if you have a history of heart problems or if you're taking a blood pressure medication.

It's possible for Poly-Hist DM to keep you awake because it contains phenylephrine. But Poly-Hist DM also contains thonzylamine and dextromethorphan, which can both make you sleepy. Pay attention to how Poly-Hist DM affects your sleep. Contact your primary care provider to discuss better options for you if the medication is making you too sleepy or keeping you awake at night.

Avoid drinking alcohol while you're taking Poly-Hist DM. This medication contains dextromethorphan and thonzylamine, which can both cause sleepiness and dizziness. Drinking alcohol and taking Poly-Hist DM at the same time can make sleepiness and dizziness more intense. It's best to talk to your primary care provider if it isn't possible for you to avoid alcohol. They can discuss with you about ways to stop drinking. Or, they might recommend a different allergy or cold medication for you.

Poly-Hist DM isn't recommended while you're pregnant. This medication contains phenylephrine, and it's not completely clear how safe phenylephrine is during pregnancy. If you're pregnant, don't take Poly-Hist DM until you've talked to a healthcare professional first about the risks and benefits of the medication.

There isn't much information about how safe it is to take Poly-Hist DM while breastfeeding. But decongestants like phenylephrine, one of the active ingredients in Poly-Hist DM, can dry up your breast milk supply. Check with a healthcare professional before you take Poly-Hist DM if you're nursing.

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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.

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Poly-Hist DM dosage

The average cost for 1 bottle of 473ml of 10mg/5mg/25mg/5ml of Poly-Hist DM is $85.40 with a free GoodRx coupon. This is 25.78% off the average retail price of $115.07.
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DosageQuantityPrice as low asPrice per unit
473ml of 10mg/5mg/25mg/5ml1 bottle$85.40$85.40

Typical dosage 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.
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Poly-Hist DM contraindications

Contraindications are specific health conditions or situations in which a person should not take a medication due to safety concerns. If you have any of the following conditions or if any of the following apply to you, let your healthcare provider know because Poly-Hist DM will not be safe for you to take.

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What are alternatives to Poly-Hist DM?

There are a number of medications that your doctor can prescribe in place of Poly-Hist DM. Compare a few possible alternatives below.
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)
$85.40Lowest GoodRx priceView prices
Used for:

Short-term relief of symptoms from allergies and the common cold:

  • Cough from throat and lung irritation
  • Runny nose
  • Sneezing
  • Itchy or watery eyes
  • Itching of the nose or throat
  • Stuffy nose (nasal congestion)
$5.49Lowest GoodRx priceView prices
Used for:

Short-term relief of symptoms from allergies and the common cold:

  • Runny nose
  • Sneezing
  • Itchy nose or throat
  • Itchy, watery eyes
  • Cough from throat and lung irritation
  • Stuffy nose (nasal congestion)
$15.57Lowest GoodRx priceView prices

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References

Best studies we found

Borowy, 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.

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

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