Drug Information



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Brand Name
Robitussin AC
Common Name
codeine - pheniramine - guaifenesin
How does this medication work? What will it do for me?

This combination product contains three medications: codeine, pheniramine, and guaifenesin.

Codeine belongs to the group of medications called narcotic analgesics and cough suppressants. It works by blocking pain signals that are sent out by the brain to various areas of the body and reduces cough by acting in the brain to dull the cough reflex.

Pheniramine belongs to the group of medications called antihistamines, and helps to relieve sneezing and runny nose.

Guaifenesin belongs to the group of medications called expectorants. It helps to loosen mucus so it can be coughed up.

This medication is used to control cough and to help with the removal of mucus from the chest and throat when less potent medications have been tried and have failed.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

How should I use this medication?

Note: A cough is a symptom. Before taking a cough suppressant, it is important to assess the underlying cause of the cough.

The recommended dose for adults and adolescents over 12 years old is 10 mL (2 teaspoonsful) every 4 to 6 hours as needed. No more than 6 doses should be taken in a 24-hour period.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

Use an oral syringe to measure each dose of the liquid, as it gives a more accurate measurement than household teaspoons.

It is important to take this medication exactly as prescribed by your doctor. If your doctor has told you to take this medication on a regular basis and you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

What form(s) does this medication come in?

Each 5 mL of orange-coloured, cherry-flavoured syrup contains 100 mg of guaifenesin, 10 mg of codeine phosphate, and 7.5 mg of pheniramine maleate. Nonmedicinal ingredients: alcohol, caramel, citric acid, FD&C Red No. 40, FC&C Yellow No. 6, flavours, glycerin, invert sugar, sodium benzoate, and water.

Who should NOT take this medication?

Do not take this medication if you:

  • are allergic to codeine, guaifenesin, pheniramine, or any of the ingredients of the medication
  • are allergic to codeine-like narcotics
  • are at risk of blocked intestines
  • are breast-feeding
  • are experiencing slowed, shallow breathing
  • are less than 18 years of age
  • are pregnant
  • are taking an MAO inhibitor (e.g., phenelzine, tranylcypromine) or have taken one in the past 2 weeks
  • have a head injury or increased pressure inside the brain
  • have respiratory problems, such as chronic obstructive pulmonary disease or asthma
  • have seizures
  • have active alcoholism or are experiencing alcohol withdrawal
What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • constipation
  • decreased appetite
  • decreased interest in sexual activity
  • dizziness
  • drowsiness
  • dry mouth
  • headache
  • nausea
  • trouble sleeping
  • vomiting
  • weakness

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • agitation
  • coordination problems
  • fainting
  • hallucinations (seeing, hearing, or feeling things that are not there)
  • increased or irregular heartrate
  • increased sweating
  • itchiness
  • severe constipation
  • signs of breathing problems (e.g., shortness of breath, wheezing, irregular or troubled breathing)
  • skin rash
  • vision changes

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • seizures
  • signs of a serious allergic reaction (i.e., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
  • signs of too much codeine (overdose):
    • cold, clammy skin
    • low blood pressure
    • pinpoint pupils of eyes
    • severe drowsiness
    • severe nervousness or restlessness
    • slow heartbeat
    • weakness
  • symptoms of serotonin syndrome (e.g., confusion, fast heartbeat, hallucinations, restlessness, shaking, shivering, sudden jerking of muscles, sweating)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication

Abdominal conditions: Codeine, like other narcotic medications may make the diagnosis of abdominal conditions more difficult or it may worsen these conditions. If you are scheduled for abdominal surgery or have an abdominal condition such as inflammatory or obstructive bowel disease, acute cholecystitis, or pancreatitis, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Accidental use: When this medication is used by anyone other than the person for whom it was prescribed, the effects of the medication may be fatal. Keep this medication out of sight and reach of children.

Adrenal gland problems: Adrenal glands produce chemical messengers that are responsible for the normal function of the body’s organs, including how your body responds to injury or stress. When opioids are taken for a month or longer, the medication may cause your adrenal gland to function improperly. Your doctor may monitor your adrenal gland condition especially if you have experienced stress such as surgery, injury, or severe infection.

Alcohol and other medications that cause drowsiness: Do not combine this medication with alcohol or other medications that cause drowsiness (e.g., antidepressants, sleeping pills, anxiety medications) since additive drowsiness can occur and be dangerous.

Breathing: Codeine can suppress breathing. Children are more likely to experience serious breathing problems, including death. For this reason, this medication should not be given to people less than 18 years old. If you are at risk for breathing difficulties, such as asthma, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Constipation: Codeine can be very constipating. Eating a high-fibre diet and following good bowel habits will help to minimize this effect. If you develop constipation easily, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Dependence and withdrawal: This medication contains codeine. Physical dependence, psychological dependence, and abuse have occurred with the use of codeine. People with a history of past or current substance use problems may be at greater risk of developing abuse or addiction while taking this medication. Abuse is not a problem with people who require this medication for pain relief.

If you suddenly stop taking this medication, you may experience withdrawal symptoms such as anxiety, sweating, trouble sleeping, shaking, pain, nausea, tremors, diarrhea, and hallucinations. If you have been taking this medication for a while, it should be stopped gradually as directed by your doctor.

Diabetes: This medication contains sugar, which may increase blood glucose levels. It may become necessary to test your blood glucose levels more often when taking codeine–pheniramine–guaifenesin.

If you have diabetes, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Drowsiness/reduced alertness: This medication may cause drowsiness. Do not drive, operate machinery, or perform other potentially hazardous tasks until you know how this medication affects you.

Glaucoma: Codeine–pheniramine–guaifenesin may make glaucoma worse. If you have narrow-angle glaucoma, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Head injury: If you have a head injury or increased pressure in the head, you may have a higher risk of experiencing side effects (breathing problems) or worsening of their condition while taking this medication. Discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Heart disease: This medication may make symptoms of certain heart conditions worse. If you have irregular heart rhythm, ischemic heart disease, high blood pressure, or another heart condition, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Kidney function: If you have kidney disease or reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Acetaminophen can cause decreased liver function. If you have liver disease or reduced liver function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Other medical conditions: The medications in codeine–pheniramine–guaifenesin can have an effect on other medical conditions. The codeine may make symptoms of delirium tremens or acute alcohol intoxication worse.

As well, this medication may cause symptoms of low thyroid (hypothyroidism), Addison's disease, benign prostatic hypertrophy (enlarged prostate), gallbladder disease, urethral stricture, decreased function of the adrenal glands, or porphyria, to become worse. If you have any of these conditions, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Serotonin syndrome: Although rare, severe reactions are possible when codeine is combined with other medications that act on serotonin, such as tricyclic antidepressants and serotonin reuptake inhibitors, medications used to treat depression. These combinations should be avoided if possible. Symptoms of a reaction may include muscle rigidity and spasms, difficulty moving, changes in mental state including delirium and agitation. Coma and death are possible.

If you are taking antidepressants, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Seizures: If you have seizures or have a history of seizure disorders, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately. Infants born to  parents who have been taking codeine for long periods of time or who are physically dependent on codeine will also be physically dependent on the medication and may experience breathing difficulties as well as withdrawal symptoms.

Breast-feeding: This medication passes into breast milk. Some of the codeine dose is converted into morphine by the body, once it has been taken. For some people, this change happens much faster than for others. If this happens to a nursing parent, the baby is a risk of receiving a morphine overdose through the breast milk.

If you are breast-feeding and are taking codeine–pheniramine–guaifenesin, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: Children may be more likely to experience severe side effects of medications for cough and cold. As a result, this medication is not recommended for children under 18 years of age

Seniors: Seniors may be more susceptible to the harmful effects of the medicines in this product.

What other drugs could interact with this medication?

There may be an interaction between codeine–pheniramine–guaifenesin and any of the following:

  • "azole” antifungals (e.g., fluconazole, itraconazole, ketoconazole)
  • abiraterone acetate
  • acetylcholinesterase inhibitors (e.g., donepezil, galantamine, neostigmine, rivastigmine)
  • aclidinium
  • alcohol
  • amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
  • antihistamines (e.g., cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine)
  • antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
  • apalutamide
  • aprepitant
  • atropine
  • barbiturates (e.g., phenobarbital, butalbital)
  • benzodiazepines (e.g., diazepam, lorazepam, oxazepam)
  • benztropine
  • betahistine
  • bosentan
  • botulinum toxin
  • brimonidine
  • bromocriptine
  • buprenorphine
  • bupropion
  • cannabis
  • carbonic anhydrase inhibitors (e.g., acetazolamide, methazolamide)
  • chloral hydrate
  • cinacalcet
  • clidinium
  • cobicistat
  • darifenacin
  • desmopressin
  • diltiazem
  • diphenoxylate
  • disopyramide
  • diuretics (water pills; e.g., furosemide, hydrochlorothiazide, triamterene)
  • domperidone
  • dronedarone
  • efavirenz
  • entacapone
  • enzalutamide
  • ethopropazine
  • etravirine
  • eplerenone
  • entacapone
  • fesoterodine
  • flibanserin
  • flunarizine
  • general anesthetics (medications used to put people to sleep before surgery)
  • glucagon
  • glycopyrrolate
  • grapefruit juice
  • ipratropium
  • HIV protease inhibitors (e.g., atazanavir, darunavir, ritonavir)
  • kava kava
  • ketamine
  • ketotifen
  • lemborexant
  • letermovir
  • linezolid
  • lithium
  • lumacaftor and ivacaftor
  • methadone
  • metoclopramide
  • mifepristone
  • minocycline
  • mirabegron
  • mirtazapine
  • modafinil
  • monoamine oxidase inhibitors (MAOIs; e.g., moclobemide, rasagiline, phenelzine, selegiline, tranylcypromine)
  • muscle relaxants (e.g., baclofen, cyclobenzaprine, methocarbamol, orphenadrine)
  • nabilone
  • naltrexone
  • other narcotic pain relievers (e.g., butorphanol, fentanyl, hydrocodone, morphine)
  • oxybutynin
  • peginterferon alfa 2-b
  • pegvisomant
  • perampanel
  • pitolisant
  • pizotifen
  • pomalidomide
  • pramipexole
  • pregabalin
  • propiverine
  • protein kinase inhibitors (e.g., ceritinib, imatinib, nilotinib)
  • quinine
  • rifabutin
  • rifampin
  • ritonavir
  • ropinirole
  • rotigotine
  • scopolamine
  • St. John's wort
  • scopolamine
  • selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, duloxetine, fluoxetine, paroxetine, sertraline)
  • serotonin/norepinephrine reuptake inhibitors (SNRIs; e.g., desvenlafaxine, duloxetine, venlafaxine)
  • seizure medications (e.g., carbamazepine, clobazam, levetiracetam, phenytoin, primidone, topiramate, valproic acid)
  • sodium oxybate
  • solifenacin
  • somatostatin analogues (e.g., lanreotide, octreotide, pasireotide)
  • spironolactone
  • terbinafine
  • tetrabenazine
  • tetrahydrocannabinol
  • thalidomide
  • tiotropium
  • tolterodine
  • trazodone
  • tricyclic antidepressants (e.g., amitriptyline, desipramine, nortriptyline)
  • trihexyphenidyl
  • trospium
  • tryptophan
  • umeclidinium
  • tryptophan
  • umeclidinium
  • valerian
  • verapamil
  • zolpidem
  • zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

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