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Benzoic acid

Generic Name: Methenamine, Phenyl Salicylate, Methylene Blue, Benzoic Acid, Hyoscyamine (meth EN a meen, fen nil sa LIS i late, METH i leen bloo, ben ZOE ik AS id & hye oh SYE a meen)
Brand Name: Hyophen, Prosed/DS, Urophen MB
Easy-to-read patient leaflet for Methenamine, Phenyl Salicylate, Methylene Blue, Benzoic Acid, Hyoscyamine. Includes indications, proper use, special instructions, precautions, and possible side effects.
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Drug Information:
This is not a list of all drugs or health problems that interact with methenamine, phenyl salicylate, methylene blue, benzoic acid, hyoscyamine. Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take methenamine, phenyl salicylate, methylene blue, benzoic acid, hyoscyamine with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor. Learn more

Benzoic acid Side Effects

Benzoic acid / hyoscyamine / methenamine / methylene blue / phenyl salicylate Side Effects

For the Consumer

Applies to benzoic acid/hyoscyamine/methenamine/methylene blue/phenyl salicylate: 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.
  • Shortness of breath.
  • Not able to pass urine.
  • A fast heartbeat.
  • Blurred eyesight.
  • Very bad dizziness or passing out.
  • A severe and sometimes deadly problem called serotonin syndrome may happen if you take this drug with certain other drugs. Call your doctor right away if you have agitation; change in balance; confusion; hallucinations; fever; fast or abnormal heartbeat; flushing; muscle twitching or stiffness; seizures; shivering or shaking; sweating a lot; severe diarrhea, upset stomach, or throwing up; or severe headache.

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:

  • Upset stomach or throwing up.
  • Dry mouth.
  • Change in color of urine or stool to blue or green.
  • Flushing.
  • Dizziness.
  • Feeling sleepy.

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 http://www.fda.gov/medwatch.

For Healthcare Professionals

Applies to benzoic acid / hyoscyamine / methenamine / methylene blue / phenyl salicylate: oral tablet


Frequency not reported: Blue to blue-green discoloration of the urine, difficult micturition, acute urinary retention


Frequency not reported: Tachycardia, flushing


Rare (less than 0.1%): Itching, rash, swelling


Frequency not reported: Blue to blue-green discoloration of stools, dry mouth, nausea, vomiting

Nervous system

Frequency not reported: Dizziness, drowsiness


Rare (less than 0.1%): Allergic reaction (i.e., itching, rash, severe dizziness, swelling, trouble breathing)


Rare (less than 0.1%): Dyspnea


Frequency not reported: Blurred vision

Editorial References and Review

Medically reviewed by BestRx Medical Team Last updated on 1/1/2020.

Source: Drugs.com Benzoic Acid