Can Methenamine and Vitamin C Help Prevent Urinary Tract Infections (UTIs)?

Urinary tract infections (UTIs) are common infections, especially as you age. You can easily treat most simple UTIs with antibiotics. But, for some people, the infections may become frequent — three or more in a year. 

For recurrent UTIs, treatments like methenamine with vitamin C (ascorbic acid) may decrease the risk of infections. But there’s limited and mixed evidence that vitamin C alone may help treat or prevent UTIs. 

Does vitamin C alone prevent UTIs?

Many people use 100 mg of vitamin C daily as a supplement to prevent UTIs. But it isn’t a proven treatment. There’s mixed data on vitamin C alone as an effective treatment for UTIs. 

There’s some lab research that shows vitamin C may prevent the growth of some bacteria. But studies haven’t proven this in people yet. So experts don’t recommend vitamin C to prevent or treat UTIs.

What is methenamine?

Methenamine (Hiprex) is an antibiotic that people often use to prevent UTIs from happening in the first place. But it’s different from other antibiotics that treat active UTIs. 

Most UTI treatments kill the bacteria that are causing an infection. Methenamine decreases bacteria in the urine by producing formaldehyde in the urinary tract. This doesn’t kill the bacteria, but it prevents bacteria from growing in the urine. 

Methenamine may help prevent recurrent UTIs when more common antibiotics don’t work. 

Should you take methenamine with vitamin C?

Some people take vitamin C along with methenamine to prevent UTIs. That’s because vitamin C may help make urine more acidic. And methenamine works best when your urine is acidic. In fact, it won’t form formaldehyde unless the urine pH reaches a highly acidic level. 

There’s mixed data on how effective this treatment is. But 1 g to 4 g of vitamin C may have some benefits when taken with methenamine. It may work to enhance the effect of methenamine on decreasing bacteria in the urine. 

EXPERT PICKS: WHAT TO READ NEXT

• Having female anatomy means more risk of a urinary tract infection (UTI): Find out more about UTI causes, symptoms, and treatments in women. 

• Think you’ve got a UTI? Here are steps you can take to get rid of a UTI fast.

• Who gets a UTI, and what causes it? Learn about the common causes of UTI and who’s most at risk.

How do you use methenamine?

Methenamine is approved for long-term use in people who are at risk for recurrent UTIs. And it’s also safe for use in children over 6 years old with recurrent infections. 

Depending on the formulation, people typically take one of the following:

• 500 mg: twice a day 

• 1,000 mg: 4 times a day

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How long you need to take it can vary from person to person. 

It’s important to note that methenamine isn’t recommended for an active infection. That’s because it doesn’t work to kill bacteria. Rather, it works by preventing further growth of bacteria. 

So, you’ll need more traditional antibiotics to treat an active UTI. Your prescriber will discuss your treatment options with you and determine if methenamine is a good choice for you. 

What are the benefits of methenamine?

If you get UTIs often and take antibiotics for them, the bacteria can start to resist the antibiotics. This means the medication won’t help your UTI. 

This problem shows up the most with standard antibiotic treatments like: 

• Sulfamethoxazole / trimethoprim

• Ciprofloxacin

• Nitrofurantoin

But with methenamine, the risk of antibiotic resistance is lower. This means you can take methenamine for longer periods of time without developing antibiotic resistance.

Are there any side effects of methenamine?

In general, methenamine is safe to use. But, as with any medication, there’s a risk of side effects with methenamine. 

Most side effects are related to the gastrointestinal (GI) system. You can sometimes avoid this by taking the medication with food. 

Potential side effects from methenamine include:

• Nausea

• Vomiting

• Stomach cramps

• Diarrhea

• Loss of appetite

• Rash

Methenamine may also cause issues if you have certain underlying conditions. You should let your prescriber know if you have:

• Allergy to aspirin

• Liver disease (like cirrhosis)

• Kidney disease

• Gout

• Plans to become pregnant

Which antibiotics should you try before methenamine to prevent UTIs?

To prevent UTIs, you have several medication options. To help you choose, it’s best to speak with a healthcare professional. They’ll take a few things into account when choosing a medication that’s right for you:

• Your medical history

• The bacteria in your previous infections

• The treatment that worked best (or not)

• Any allergies or potential interactions to have to medications 

Preferred treatment for UTI prevention often includes: 

• Nitrofurantoin

• Trimethoprim

• Cephalexin

If these medications haven’t worked for you to prevent UTIs, then methenamine might be a good option to try. 

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Written by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Frank Schwalbe, MD

Frank Schwalbe, MD, is an assistant professor of anesthesiology at the Yale School of Medicine. He has practiced anesthesiology for 30 years.

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