By Medically reviewed by Hello Doktor Medical Panel


What is Synflex® (naproxen sodium) used for?

Synflex® is commonly used to relieve mild to moderate pain, signs and symptoms of mild to moderately severe, acute or chronic, musculoskeletal & soft tissue inflammation, acute gout.

How should I take Synflex® (naproxen sodium)?

Use Synflex® exactly as directed on the label, or as prescribed by your doctor. Do not take this medicine in larger amounts or for longer than recommended. Use the lowest dose that is effective in treating your condition.

Do not crush, chew, or break a tablet. Swallow it whole.

Shake the oral suspension (liquid) well just before you measure a dose. Measure liquid medicine with the dosing syringe provided, or with a special dose-measuring spoon or medicine cup. If you do not have a dose-measuring device, ask your pharmacist for one.

If you change brands, strengths, or forms of Synflex®, your dosage needs may change. Ask your pharmacist if you have any questions about the type of medicine you are using.

If a child is using this medicine, tell your doctor if the child has any changes in weight. Synflex® doses are based on weight in children, and any changes may affect your child’s dose.

If you use Synflex® long-term, you may need frequent medical tests.

This medicine can cause unusual results with certain medical tests. Tell any doctor who treats you that you are using Synflex®.

How do I store Synflex® (naproxen sodium)?

Synflex® is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store Synflex® in the bathroom or the freezer. There may be different brands of Synflex® that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush Synflex® down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using Synflex® (naproxen sodium)?

Before using this drug, tell your doctor if:

  • You are pregnant or breastfeeding. This is because, while you are expecting or feeding a baby, you should only take medicines on the recommendation of a doctor.
  • You are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • You have allergy with any of active or inactive ingredients of Synflex® or other medications.
  • You have any other illnesses, disorders, or medical conditions.

Synflex® can increase your risk of fatal heart attack or stroke, especially if you use it long term or take high doses, or if you have heart disease. Even people without heart disease or risk factors could have a stroke or heart attack while taking this medicine.

Do not use this medicine just before or after heart bypass surgery (coronary artery bypass graft, or CABG).

Synflex® may also cause stomach or intestinal bleeding, which can be fatal. These conditions can occur without warning while you are using Synflex®, especially in older adults.

You should not use Synflex® if you have ever had an asthma attack or severe allergic reaction after taking aspirin or an NSAID.

Is it safe during pregnancy or breastfeeding?

There isn’t enough information about the safety of using Synflex® during pregnancy and breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking Synflex®.

Side effects

What side effects can occur from Synflex® (naproxen sodium)?

Common side effects may include:

  • Indigestion
  • Heartburn
  • Stomach pain
  • Nausea
  • Diarrhea
  • Constipation
  • Headache
  • Dizziness
  • Drowsiness
  • Swelling in your hands or feet
  • Bruising
  • Itching
  • Rash
  • Sweating
  • Ringing in your ears

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.


What drugs may interact with Synflex® (naproxen sodium)?

Synflex® may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs, and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Products that may interact with this drug are:

  • Lithium
  • Methotrexate
  • Probenecid
  • A blood thinner (warfarin, Coumadin, Jantoven)
  • Heart or blood pressure medication, including a diuretic or “water pill”
  • Steroid medicine (such as prednisone)

Does food or alcohol interact with Synflex® (naproxen sodium)?

Synflex® may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with Synflex® (naproxen sodium)?

Synflex® may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.

Health conditions that may interact with this drug are:

  • Heart disease
  • High blood pressure
  • High cholesterol
  • Diabetes
  • Smoke
  • A history of heart attack, stroke, or blood clot
  • A history of stomach ulcers or bleeding;
  • Asthma
  • Liver or kidney disease
  • Fluid retention


The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using Synflex® (naproxen sodium).

What is the dose of Synflex® (naproxen sodium) for an adult?


Immediate Release Tablets and Suspension: The recommended dose is 250 mg to 500 mg or 275 mg to 550 mg orally twice a day.

Rheumatoid Arthritis

Immediate Release Tablets and Suspension: The recommended dose is 250 mg to 500 mg or 275 mg to 550 mg orally twice a day.


Immediate Release: The recommended dose is 550 mg orally once, followed by 275 mg orally every 6 to 8 hours or 550 mg orally every 12 hours as needed.

Fever – OTC

The recommended dose is 220 mg orally every 8 to 12 hours while symptoms persist.

What is the dose of Synflex® (naproxen sodium) for a child?

Fever – OTC

12 years or older: The recommended dose is 220 mg orally every 8 to 12 hours while symptoms persist.

Pain – OTC

12 years or older: The recommended dose is 220 mg orally every 8 to 12 hours while symptoms persist.

How is Synflex® (naproxen sodium) available?

Synflex® is available in the following dosage forms and strengths:

  • Tablet

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of Synflex®, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.

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Review Date: June 20, 2017 | Last Modified: December 19, 2019

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