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About Guaifenesin

Guaifenesin with Dextromethorphan combination medication is used to temporarily treat coughing and chest congestion symptoms caused by the common cold, flu, or other breathing illnesses (e.g., sinusitis, bronchitis). Guaifenesin 600 mg extended release tablets are an expectorant that helps thin and loosens mucus in the lungs, making it easier to cough up the mucus. Didex 400 is an opioid cough suppressant (antitussive) that affects a certain part of the brain, reducing the urge to cough. Guaifenesin in pregnancy is not usually used for ongoing coughs from smoking, asthma, other long-term breathing problems (e.g., emphysema), or for coughs with a lot of mucus unless directed by your doctor. Guaifenesin breastfeeding is okay to be taken.

Opioid cough suppressants should not be used in children younger than 18 years. Children are at higher risk for serious (even fatal) side effects, especially breathing problems. Talk with the doctor about the risks and benefits of this medication.

cough-and-cold products do not cure colds. Cough due to a common cold often does not need to be treated with medicine. Ask your doctor or pharmacist about other ways to relieve cough and cold symptoms, such as drinking enough fluids, using a humidifier, or saline nose drops/spray.

How to use

  • Take Guaifenesin with Dextromethorphan by mouth with or without food.
  • Usually, every 4 to 6 hours as needed with a full glass of water.
  • Didex 400 can be taken with food if a stomach upset occurs.
  • Drink plenty of fluids while you are using this medication unless otherwise directed by your doctor.
  • The fluid will help loosen the mucus in your lungs.
  • If you are using the liquid form of Guaifenesin 600 mg extended release tablets, carefully measure the dose using a special measuring device/spoon.
  • Do not use a household spoon because you may not get the correct dose.

Some liquids need to be shaken before pouring each dose. Check your bottle or ask your pharmacist if your product needs to be shaken.

Do not increase your dose or use Guaifenesin 600 mg extended release tablets more often or for longer than prescribed. Your condition will not improve any faster, and your risk of side effects will increase.

Don’t stop abruptly

If you suddenly stop using this medication, you may have withdrawal symptoms. To help prevent withdrawal, your doctor may lower your dose slowly. Withdrawal is more likely if you have used this medication for a long time (more than a few weeks) or in high doses. Tell your doctor or pharmacist right away if you have withdrawal.

Though it helps many people, Guaifenesin with Dextromethorphan has a risk for abuse and may sometimes cause addiction. This risk may be higher if you have a substance use disorder (such as overuse of or addiction to drugs/alcohol). Take this product exactly as prescribed to lower the risk of addiction. Ask your doctor or pharmacist for more details.

When used for an extended time, Didex 400 may not work as well and may require different dosing. Talk with your doctor if this medication stops working well.

Tell your doctor if your cough does not get better in 5 days. Also, tell your doctor if your condition gets worse, or if you have a fever, rash, or persistent headache. These may be symptoms of a serious medical problem and should be checked by a doctor.

Side effects

  • Drowsiness
  • dizziness
  • lightheadedness
  • facial flushing
  • nausea
  • vomiting
  • constipation

If any of these Didex 400 effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using Guaifenesin with Dextromethorphan do not have serious side effects.

Some serious and rare side effects

Tell your doctor right away if you have any serious side effects, including interrupted breathing during sleep (sleep apnea), mental/mood changes (e.g., hallucinations), fast/irregular heartbeat, trouble urinating.

Get medical help right away if you have any very serious side effects, including seizures.

Codeine is changed into a strong opioid drug (morphine) in your body. In some people, this change happens faster and more completely than usual, which increases the risk of very serious Guaifenesin 600 mg extended release tablets side effects. Get medical help right away if you notice any of the following: slow/shallow breathing, severe drowsiness/difficulty waking up, confusion.

A very serious allergic reaction to Guaifenesin with Dextromethorphan is rare. However, get medical help right away.

Warnings & Precautions

  1. Before taking Didex 400, tell your doctor or pharmacist if you are allergic to it.
  2. Before using Guaifenesin 600 mg extended release tablets, tell your doctor or pharmacist your medical history.
  3. Do not drive, use machinery, or do anything that needs alertness until you can do it safely.
  4. Avoid alcoholic beverages.
  5. Tell your doctor if you are pregnant or think you may be pregnant.

To reduce dizziness and lightheadedness, get up slowly when rising from a sitting or lying position.

Liquid forms of this medication may contain sugar, alcohol, or aspartame. Caution is advised if you have diabetes, alcohol dependence, liver disease, phenylketonuria (PKU), or any other condition that requires you to monitor/avoid these substances in your diet. Consult your doctor or pharmacist about using this medication safely.

Older adults may be more sensitive to the side effects of this drug, especially confusion, dizziness, drowsiness, and slow/shallow breathing.

Guaifenesin in pregnancy is not recommended. Guaifenesin in pregnancy may harm an unborn baby. Talk to your doctor about the risks and benefits of Guaifenesin in pregnancy.

Guaifenesin breastfeeding passes into breast milk and may have undesirable effects on a nursing infant (such as unusual sleepiness, difficulty feeding, trouble breathing, or unusual limpness). Guaifenesin breastfeeding is not recommended. Consult your doctor before Guaifenesin breastfeeding.


Store at room temperature away from light and moisture. Do not store in the bathroom. Do not freeze liquid forms of this medication. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Consult your pharmacist or local waste disposal company.

Drug interactions

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor’s approval.

Some products that may interact with this drug include cimetidine, naltrexone.



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