Is expired penicillin safe to take?

Quick Answer

Taking expired penicillin can be risky. Penicillin, like most medications, can become less effective and more likely to cause side effects when it’s past its expiration date. However, expired penicillin may still provide some benefit if taken within a year or two of expiration. To be safe, always check with your pharmacist or doctor before taking any expired medication.

What Happens When Penicillin Expires?

Penicillin is an antibiotic used to treat bacterial infections. It works by interfering with the formation of the bacterial cell wall, weakening the bacteria’s protective barrier and causing them to die.

Like all medications, penicillin begins to break down over time. Exposure to heat, humidity, and temperature fluctuations hastens this process. The active ingredient may start to degrade within a couple years of the expiration date.

An expired penicillin medication may have the following issues:

  • Reduced potency – The drug may not be as effective at killing bacteria.
  • Change in chemical composition – Degraded and potentially toxic by-products may form.
  • New side effects – Decomposition products may cause adverse reactions not associated with the active drug.
  • Change in color/smell/texture – The physical appearance and properties of the drug may change.

So while taking an expired penicillin pill might provide some antibiotic effect, there are definite risks involved.

How Long After Expiration is Penicillin Still Effective?

Studies show mixed findings on how long after expiration penicillin retains its potency. Much depends on storage conditions. Recommendations vary:

  • Within 1 year past expiration: The medication has likely retained most of its original potency and is considered generally safe to take.
  • Within 2 years of expiration: Potency may be reduced to 88% of original strength according to some sources, but chance of full efficacy makes it potentially worth using.
  • 2-3 years past expiration: Up to 80% potency may remain, but risk of degradation and side effects increases.
  • Over 3 years: Drug may be significantly less effective and more risky. Should be discarded.

Liquid forms of penicillin tend to degrade faster than tablets. And storage conditions make a big difference. Keeping medications in a cool, dry environment will help extend their shelf life. Heat and humidity speed up chemical breakdown.

What are the Risks of Taking Expired Penicillin?

While taking expired penicillin could potentially provide some benefit, there are definite risks involved:

Reduced Effectiveness

With reduced potency, the antibiotic may not reach the minimum inhibitory concentration needed to kill off an infection. This could allow bacteria to develop resistance.

Some experts warn against using any expired antibiotics because of concerns about encouraging antibiotic resistance. Weakened drugs may destroy the weaker bacteria of an infection while leaving resistant strains intact.

Adverse Reactions

Expired medications can cause unexpected side effects from degradation products and compounds formed through oxidation. For penicillin, this could include:

  • Rashes or swelling
  • Breathing problems
  • Gastrointestinal upset like diarrhea
  • Neurological symptoms like dizziness

These new side effects occur because of changes to the chemical structure and properties of the active drug over time.

Toxic Byproducts

Besides loss of potency and efficacy, decomposition can produce potentially toxic compounds. This risk increases the longer a medication has been expired. Little research specifically looks at toxic byproducts of degraded penicillins. But it is reasonable to exercise caution with old drugs.


Superinfection refers to a new infection that occurs during or after antibiotic treatment. Weakened antibiotic potency increases risk of superinfection with resistant organisms like Clostridium difficile. This superinfection can be life-threatening.

What Types of Penicillin Can Be Taken After Expiration?

Different types of penicillin vary in their stability past expiration. Some major forms include:


Amoxicillin is a commonly prescribed penicillin. Tablets retained about 83% potency at 28 months post-expiration according to one study. Suspensions degraded faster. Risk of significantly reduced efficacy and side effects increases after about 2 years.


Ampicillin degraded faster than amoxicillin in one test, retaining only 75% potency after 16 months post-expiration. Other estimates say ampicillin tablets are likely effective within about 1 year of expiration.

Penicillin VK

Penicillin VK tablets may lose around 5% potency per year. One source says up to 90% potency may remain even after 2 years past expiration. But it’s still best to discard tablets over a year old.

Injection forms of penicillin tend to lose potency faster than oral tablets. Penicillin G injections might be effective up to about 1 year past expiration. After that toxic byproducts and superinfections become a concern.

Check any penicillin containers for signs of change like discoloration or crumbling before use. If expired more than 2-3 years, the antibiotic should not be used.

What About Generic Penicillin?

Studies on expired drug potency focus primarily on brand name medications. Less data is available on generic antibiotic stability. But generics likely follow similar degradation patterns.

Some experts feel generic drugs may lose potency faster after expiration than brand name equivalents due to:

  • More variability in manufacturing
  • Lower quality control standards
  • Less protective packaging

One defense department study found generic ciprofloxacin retained only 88% potency at 12 months past expiration, versus 95% for the brand name.

To be safe, generic antibiotics should likely be discarded 12 months after expiration, or earlier if any change is noticed. Be particularly cautious with generic injectable penicillins.

Can Expired Penicillin Cause More Serious Harm?

Severe allergic reactions to penicillin such as anaphylaxis are not thought to increase with expired forms of the drug. The culprit penicillin antigenic determinants don’t increase or become more allergenic over time.

However, exposure to degradation products can sometimes newly trigger an allergic reaction. This would be an allergic reaction to the byproducts, not the original antibiotic.

Beyond allergic reactions, there is no evidence that expired penicillins can cause severe harm or death when taken in normal therapeutic doses. But the risk of overdose could be greater if the potency is higher than expected.

As a safety precaution, penicillin that is expired by more than 2-3 years should never be taken. The risks start to clearly outweigh any possible benefits.

Can You Test if Expired Penicillin is Still Potent?

There is no easy way to assess the potency of an expired penicillin short of laboratory testing. But there are some basic things you can look for:

Check Physical Appearance

Look closely at the color and physical integrity of pills or liquid. Signs of change like spots, crumbling, cloudiness, or crystallization mean the drug has degraded and should not be used.


There should be little to no odor with penicillin. A strong medicinal or chemical smell means decomposition has occurred.

Look for Labeling

Some outdated prescriptions still have percentage of potency marked on the label. A listing of less than 90% potency means the antibiotic should be discarded.

Research Manufacturer Standards

Some drug companies claim to use higher quality or overfill standards so products exceed shelf life expectations. But never rely on this alone.

While these basic tests can sometimes weed out clearly degraded penicillin, they cannot confirm an expired drug is fully potent and stable. When in doubt, do not take chances with old antibiotics.

How Should You Dispose of Expired Penicillin?

Outdated or unused penicillin should be properly disposed of. Avoid flushing down the toilet or sink, as antibiotic residues can persist in the environment and promote resistance. Recommended disposal methods include:

  • Community drug take-back programs
  • Household hazardous waste collection
  • Mixing with coffee grounds or kitty litter before sealed in bag and trash can
  • Some pharmacies offer disposal

Removing unnecessary expired antibiotics from the home protects you and the environment.

Can a Pharmacist Advise if Expired Penicillin is Ok?

You should never take expired medication without checking with a pharmacist or doctor first. Pharmacists have expert training in how drugs break down over time. They can provide the best, individualized advice in assessing an outdated penicillin product.

Be prepared to tell the pharmacist:

  • The type of penicillin
  • The original expiration date
  • How it was stored
  • Any changes to its look, smell, etc.

Based on the circumstances, a pharmacist can counsel you on whether taking the expired penicillin might be prudent or not worth the risk. If the antibiotic is deemed questionable, have it replaced.

Do not rely on home testing or rule of thumb estimates. Always consult an expert like a pharmacist when considering use of expired medications.

Can a Doctor Write a Prescription for Expired Penicillin?

Doctors are unlikely to issue a prescription for a medication they know is expired. Doing so would be unethical and encourage use of a drug outside the limits of stability data.

However, a physician might provide guidance on use of expired antibiotics in an emergency situation where no alternatives exist. Otherwise, they will recommend discarded expired penicillins be replaced with a new prescription.

Before taking any expired medication, it’s important to have both a pharmacist and doctor review it if possible. This provides the most thorough, objective assessment of appropriateness.

Is it Legal to Take or Possess Expired Penicillin?

There are no laws prohibiting possession or use of expired over-the-counter medications like amoxicillin. However, it is technically illegal to take or possess expired prescription penicillins without a valid prescription. This includes:

  • Using leftover antibiotics prescribed for someone else
  • Keeping unused expired penicillin without ongoing prescription
  • Taking old antibiotics without consulting a physician

Charges are rarely brought against those using expired antibiotics. But the safest way to take any prescription penicillin is to first get physician and pharmacist approval.

As a prescription drug, you should not take expired penicillin without some type of medical authorization. This helps ensure appropriate, ethical use.

When Can Expired Penicillin Be Safely Taken?

Taking expired penicillin always carries some degree of risk. But in certain circumstances it may be warranted:

Life-Threatening Infection

For a severe infection when no other antibiotic options are available, an expired penicillin might be used as a last resort with doctor oversight.

Verified Potency

If laboratory testing confirms adequate potency (90% or more), an expired penicillin could potentially be used short-term.

Oral and Noncritical Use

An oral tablet taken for a mild, non-life threatening infection has lower risk if used soon after expiration and stored properly.

Emergency Scenarios

In crises like disasters when new prescriptions are unavailable, use of recently expired drugs may need to be considered.

While taking expired antibiotics is rarely recommended, there are limited cases where the small risks might be acceptable. Always consult a pharmacist first. Never use expired injectable penicillin.

Key Points About Expired Penicillin

  • Expired penicillin can become less potent, less effective, and more likely to cause side effects.
  • Oral tablets may retain some potency within 1-2 years of expiration, but are still risky.
  • Injected penicillin degrades faster and should not be used if expired.
  • Seek pharmacist or doctor guidance before using any expired antibiotic.
  • Discard penicillin expired by more than 2-3 years; do not take chances.
  • Never use clearly discolored or degraded expired penicillin.

The Bottom Line

While taking recently expired penicillin is sometimes viewed as harmless, doing so does pose real risks to health and antibiotic resistance. The prudent approach is to properly discard outdated penicillin and get a new prescription. But in limited cases, a pharmacist may advise that taking expired penicillin is reasonable. Always seek expert consultation before taking any medication past its expiration date.

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