Cough syrup side effects

Mucinex Fast-Max Cold, Flu & Sore Throat Side Effects

Generic Name: acetaminophen / dextromethorphan / guaifenesin / phenylephrine

Medically reviewed by Last updated on Jul 30, 2019.

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Note: This document contains side effect information about acetaminophen / dextromethorphan / guaifenesin / phenylephrine. Some of the dosage forms listed on this page may not apply to the brand name Mucinex Fast-Max Cold, Flu & Sore Throat.

For the Consumer

Applies to acetaminophen / dextromethorphan / guaifenesin / phenylephrine: oral capsule, oral liquid, oral tablet

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Signs of liver problems like dark urine, feeling tired, not hungry, upset stomach or stomach pain, light-colored stools, throwing up, or yellow skin or eyes.
  • Not able to pass urine or change in how much urine is passed.
  • A very bad skin reaction (Stevens-Johnson syndrome/toxic epidermal necrolysis) may happen. It can cause very bad health problems that may not go away, and sometimes death. Get medical help right away if you have signs like red, swollen, blistered, or peeling skin (with or without fever); red or irritated eyes; or sores in your mouth, throat, nose, or eyes.

What are some other side effects of this drug?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

  • Dizziness.
  • Feeling nervous and excitable.
  • Not able to sleep.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-FDA-1088. You may also report side effects at

For Healthcare Professionals

Applies to acetaminophen/dextromethorphan/guaifenesin/phenylephrine: oral capsule, oral liquid, oral powder for reconstitution, oral tablet


The manufacturer has not provided adverse event information.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

Medical Disclaimer

More about Mucinex Fast-Max Cold, Flu & Sore Throat (acetaminophen / dextromethorphan / guaifenesin / phenylephrine)

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  • Imprints, Shape & Color Data
  • Drug Interactions
  • Pricing & Coupons
  • Drug class: upper respiratory combinations
  • FDA Alerts (5)

Consumer resources

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Other Information: Each 20 ml contains: sodium 12 mg. Store between 68-77 degrees F (20-25 degrees C). Dosing cup provided. Do not refrigerate. Misc: For ages 12+. Maximum strength (per 4-hour dose). Acetaminophen – pain reliever/fever reducer. Dextromethorphan HBr – cough suppressant. Guaifenesin – expectorant. Phenylephrine HCl – nasal decongestions. Relievers headache, fever & sore throat. Controls cough. Relieves nasal & chest congestion. Thins & loosens mucus. See new information. Parents: Learn about teen medicine abuse. Questions? 1-866-Mucinex (1-866-682-4639). You may also report side effects to this phone number. Health. Hygiene. Home. Please visit our web site


Warnings: Allergy alert: Acetaminophen may cause severe skin reactions. Symptoms may include: skin reddening; blisters; rash. If a skin reaction occurs, stop use and seek medical help right away. Liver warning: This product contains acetaminophen. Severe liver damage may occur if you take: more than 6 doses in 24 hours, which is the maximum daily amount; with other drugs containing acetaminophen; 3 or more alcoholic drinks daily while using this product. Sore throat warning: If sore throat is severe, persists for more than 2 days, is accompanied or followed by fever, headache, rash, nausea, or vomiting, consult a doctor promptly. Do not use: with any other drug containing acetaminophen (prescription or nonprescription) (If you are not sure whether a drug contains acetaminophen, ask a doctor or pharmacist); 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 do not know if your prescription drug contains an MAOI, ask a doctor or pharmacist before taking this product. Ask a doctor before use if you have liver disease; heart disease; diabetes; high blood pressure; thyroid disease; trouble urinating due to an enlarged prostate gland; persistent or chronic cough such as occurs with smoking, asthma, chronic bronchitis, or emphysema; cough that occurs with too much phlegm (mucus). Ask a doctor or pharmacist before use if you are taking the blood thinning drug warfarin. When using this product: do not use more than directed. Stop use and ask a doctor if: nervousness, dizziness, or sleeplessness occur; pain, nasal congestion, or cough gets worse or lasts more than 7 days; fever gets worse or lasts more than 3 days; redness or swelling is present; new symptoms occur; cough comes back, or occurs with rash or headache that lasts. These could be signs of a serious condition. Pregnancy/breast-feeding warning: If pregnant or breast-feeding, ask a health professional before use. Keep out of reach of children. Overdose Warning: Taking more than the recommended dose (overdose) may cause liver damage. In case of overdose, get medical help or contact a Poison Control Center right away. Quick medical attention is critical for adults as well as for children even if you do not notice any signs or symptoms. Other warnings: Tamper Evident: Do not use if neckband on bottle cap is broken or missing.

Cough and Cold Medicine Abuse

When people take too much DXM, they might have hallucinations and “out-of-body” sensations. DXM also depresses brain function, particularly the parts of the brain that control breathing and heart function.

Taking a lot of DXM causes hallucinations and out-of-body sensations similar to the ones caused by drugs like ketamine and PCP. These effects can last as long as 6 hours.

DXM also can make users have trouble controlling their limbs and cause blurred vision, slurred speech, dizziness, and impaired judgment.

Other short-term effects include:

  • paranoia and confusion
  • excessive sweating
  • nausea and vomiting (large quantities of cough syrup almost always cause people to throw up)
  • belly pain
  • irregular heartbeat and high blood pressure
  • restlessness
  • dry, itchy skin and facial redness

DXM might seem safe since it’s sold over the counter. But large quantities can cause dangerous side effects, including loss of consciousness, seizures, brain damage, and death.

One particularly dangerous side effect of DXM is hyperthermia — extremely high fever. This is a big problem in hot environments or when DXM users physically exert themselves, like while dancing at a club. High body temperatures can quickly lead to brain damage or a coma.

It’s possible to overdose on too much DXM, especially if it’s in pure powder form. Someone who overdoses may have brain damage or seizures, and might even die.

People using cold medicines to get high may not realize they are taking high doses of many drugs, not just DXM. Mixing DXM with other drugs or alcohol increases the likelihood of life-threatening conditions. For instance, combining it with drugs like MDMA increases the risk of hyperthermia and can lead to brain damage, seizures, a coma, and death.

The Effects of Dextromethorphan Use

Dextromethorphan Effects question 2

Drug Mixtures

Dextromethorphan is common in many different kinds of cold medication sold over the counter at pharmacies and grocery stores, and is normally mixed with many different kinds of drugs. These other drugs contained in the cold medicine can be harmful to your health if taken in high dosages. For example, acetaminophen, an active ingredient in many medications, can significantly damage the liver in high doses.

In general, the most severe effects of DXM use tend to come when users intentionally combine DXM with other drugs such as stimulants, opiates and/or alcohol. For example, mixing DXM with amphetamines or cocaine can cause a dangerous rise in blood pressure and heart rate.

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Dextromethorphan Short-term Effects

“Robo-tripping,” or taking dextromethorphan in large amounts to get high, can produce short-term effect such as:

  • Euphoria/drunk feeling.
  • Sedation.
  • Detachment/dissociation.
  • Hallucinations.

DXM is increasingly recognized as a problem, especially among younger users. In fact, the Food and Drug Administration has expressed concern over the instance of abuse of this drug and the fact that pure powder forms are available for purchase on the Internet.

When DXM is snorted or injected, it can act on the body in an immediate and strong manner and can produce effects such as those seen with “dissociative anesthetic” substances, such as PCP (“Angel Dust”) and Ketamine (“Special K”).

Dextromethorphan Effects question 3

Side Effects

There are a number of different dextromethorphan side effects depending on any other chemicals the DXM might be mixed with. You may notice the following effects associated with DXM use:

  • Dizziness.
  • Feeling faint.
  • Nausea.
  • Stomach pain.
  • Restlessness.
  • Increased heart rate.
  • Fatigue.

Symptoms of a DXM Overdose

  • Vomiting.
  • Profound loss of coordination.
  • Impaired vision.
  • Difficulty breathing.
  • Irregular heart rhythm.
  • Hallucinations.
  • Dissociation.
  • Seizure.
  • Loss of consciousness.
  • Coma.

If you notice any of these signs, call for emergency treatment immediately.

Dextromethorphan Effects question 4

Long-term Effects of Dextromethorphan

The long-term effects of Dextromethorphan are not known; however, it is believed that sustained, habitual use can result in:

  • Agitation.
  • Delusions.
  • Mood changes such as depression and mania.
  • Problems with attention and memory consolidation.
  • Liver damage.

Dextromethorphan Effects question 5

Dextromethorphan Dependency

Building up a dextromethorphan tolerance is similar to any other drug; the chances of experiencing dependence and tolerance will vary depending on the frequency and dosage of each use. With regular abuse, users can develop:

  • Physical tolerance to the drug (needing more and more to experience the same intended effects).
  • Cravings for the drug.
  • Symptoms of withdrawal when not using DXM.

“Megadosing” (taking large doses) of DMX on a regular basis can quickly lead to addiction and put the user’s mental and physical health in danger.

Dextromethorphan Effects question 6

Dextromethorphan Withdrawal Treatment

Further, a survey of long-term dextromethorphan users revealed that more than half of them have experienced withdrawal symptoms, such as:

  • Fatigue.
  • Insomnia.
  • Restlessness.
  • Compulsions to get the drug.
  • Bone and muscle aches.
  • Diarrhea.
  • Impaired ability to think clearly.
  • Hypersensitivity to allergens in the environment.

While the detox process from DXM can be tough to get through, you can stop using DXM and find recovery. If you need help to get through the process, consider detoxing and seeking treatment in an inpatient rehabilitation facility where you can be assured you’ll be monitored and cared for by professionals around the clock.

If you want to learn more about the safest and best ways to withdraw and get treatment, call 1-888-744-0069Who Answers? to speak to one of our supportive treatment representatives.

Last updated on December 3, 2018 2018-12-03T23:14:36+00:00 Finding the perfect treatment is only one phone call away!

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