Can You Take Expired Bactrim?

In our latest question and answer, the pharmacist discusses whether or not it is safe to take expired Bactrim (sulfamethoxazole/trimethoprim).


I got a prescription from Bactrim DS about a year ago. I now have an infection that appears to be the same as what I used Bactrim for before. However, the prescription bottle states that the Bactrim is expired. I am wondering if it is still safe to use?

Asked by Ann Marie On Dec 26, 2021

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Dec 26, 2021
Last updated Mar 03, 2022

Key points

  • It is not recommended to take expired Bactrim as it may have lost potency over time and may not be as effective as it once was.
  • It is important to see your doctor for any new infection so it can be appropriately diagnosed and treated.

Hello and thanks for reaching out to us!

In most cases, it is not recommended to take expired medication, including expired Bactrim (Sulfamethoxazole, Trimethoprim).

Now, taking expired Bactrim generally won't cause any immediate harm, but there is the potential that it may not be effective as it once was due to a loss in potency over time.

Taking an effective medication is especially important for antibiotics. If your antibiotic has lost potency, there is a chance your infection will not be properly treated and could get worse.

Are Expired Drugs Dangerous?

Most drugs don't actually go "bad" in terms of causing harm, but they certainly may have lost potency and thus, may not have the desired effect after they expire.

So, while not dangerous in the sense they won't cause immediate physical harm after taking them, it certainly is a danger to take a medication that doesn't have the desired effect.

You certainly wouldn't want to take blood pressure or blood thinner medication that doesn't work as intended. The same goes for antibiotics. You are putting yourself at unnecessary risk by taking an expired med.

I do want to mention at the end of this section here, that there have been rare case reports of some expired drugs causing harm. One such example is a form of tetracycline available in the 1960s, which was linked to kidney damage in those taking the expired drug. 

Can You Tell A Drug Is Expired?

One of the main problems with expired drugs is that it can be difficult to tell if they have lost potency.

Some drugs, like aspirin, do show noticeable signs when they begin to break down. Expired aspirin, for example, begins to degrade into acetic acid, which has a distinct vinegar smell.

Most drugs don't have noticeable signs of degradation however and the fact of the matter is if a drug is past its listed expiration date, you just don't know it is as potent as it once was.

Expired Bactrim

In regard to Bactrim specifically, there is no published data regarding whether or not there are noticeable characteristics when it begins to degrade.

While it may be impossible to tell when Bactrim begins to degrade, there are no reports that I could find that it causes harm or adverse effects if expired, aside from not being as potent as it once was.

I really want to emphasize that you don't want to take an antibiotic that is not as potent as it once was (and this includes taking it after the expiration date). There's a real chance it won't cure your infection, putting you at risk for complications.

When Do Medications Expire?

Manufacturers typically set expiration dates 2 to 3 years from the date of manufacture, as it's a standard industry practice, and it eliminates the need to perform long, potentially expensive, stability tests. After a few years, there is just a lack of data available to make a good determination on whether or not a drug has started to degrade.

I've mentioned in a section above that it can be difficult, if not impossible, to determine the potency of expired medications. However, studies do show that most drugs take a long time to degrade to a significant extent and are generally still 'good' long after the listed expiration date.

For instance, the US military conducted a study in the 1980s on the potency of expired drugs, hoping to avoid the potential of replenishing over $100 million in soon-to-be-expiring drugs.

They found the vast majority of drugs were acceptable to use well past the labeled expiration date. This led to the 'Shelf Life Extension Program', a program that allows the stockpiling of potentially important medications past their expiration date.

This doesn't necessarily mean all expired drugs are safe to take, just that in an emergency situation with no other alternatives, they may be the best option.

Medication Storage

It is extremely important to store medications, like Bactrim, properly. The expected life span of a drug is highly dependent on proper storage. All of the following can potentially lessen the shelf life of a medication:

  • Exposure to light
  • Exposure to moisture
  • High/low temperatures

All of the above can greatly increase the degradation rate of a drug.

As there are often too many unknowns, you typically will not hear a health care professional recommend that it is OK to take any expired drug, including Bactrim. In addition, it is generally not a good idea to treat infections without seeing a doctor. 

Most infections are susceptible only to certain antibiotics. Although an infection may look the same, it may be caused by a different bacteria and should be properly diagnosed and treated by your doctor.

Final Words

I wanted to thank you again for reaching out to us!

If you do have expired Bactrim, I strongly recommend seeing your doctor for a new prescription, and to be diagnosed properly, as Bactrim may not even be the best choice for your particular problem.


  • Expiration Dating Extension, FDA
  • Bactrim Prescribing Information, AccessFDA
  • Should We Use Expired Drugs When Necessary?, PubMed
  • Drug expiry debate: the myth and the reality, PubMed
  • Are Drug Expiration Dates a Myth?, Medscape

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 11 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Feel free to send him an email at! You can also connect with Dr. Brian Staiger on LinkedIn.

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