It is possible that every household has one; a cupboard, full of leftover, expired, and unfinished medications, but when it comes to treating our pets, how important are expiration dates? Are they important?  

I mean surely, we can use an old medication for a new dog if the symptoms are the same? What about the pet that always gets ear infections, could you use the leftover drops from the last time they had the problem? 

These are all frequent questions from pet parents. The truth is that expiry dates are important. Pharmaceutical companies carry out strict testing to find out how long medications stay effective (meaning they work as they should) when kept under certain conditions, such as at a specific temperature or away from light. This testing helps them decide on an official expiration date, which tells you how long the medicine will maintain its quality and effectiveness. For instance, a common antibiotic might be evaluated to make sure it remains effective for two years if stored at room temperature and away from sunlight. 

The importance of dates 

Veterinary medications are tightly regulated for pet safety, including proper storage, use, and disposal. Expiry dates are required on labels to ensure medicines remain effective; supplying expired medications is prohibited – it’s actually illegal under the Veterinary Medicines Regulations 2013!  

A drug usually expires when its potency drops to about 90% of its original strength, which varies by type, stability, storage, and form (e.g., tablet or liquid). That said, as long as the manufacturer has tested the product for a “reasonable” time (usually about 2 years), they can put an expiry date to say that it has met the 90%+ mark, even if it’s still usable. The problem is, we don’t know which medications would still be fine, and which would not… Accurate dosing and treatment depend on reliable potency, so using medication within its expiry date is crucial. 

What about open medication?  

Expiration dates on the bottle refer to an unopened container. Once a container is opened, the expiry date can change significantly, especially with liquids or injections. This is because opening exposes the medication to air, moisture, or bacteria, which can reduce its effectiveness or safety. Always check the label or leaflet, as a new expiry date may be recommended after opening. If you cannot find one, it is best to speak to the veterinarian who dispensed your medication. If this is not possible, the general rule  is to discard all opened medication within 28 days to ensure your pet’s safety.  

Are expired products really that harmful? 

Most medications do not suddenly become harmful exactly one day after the expiration date has passed. The actual harm from using expired medications can occur in multiple ways.  

1.     Directly from the medication  

Although not all medicines break down to become toxic, it can and does happen. Over time medications can form toxic compounds that may harm your pet as it is metabolised. This is particularly true for some medications like tetracycline antibiotics, which can degrade into nephrotoxins that damage the kidneys. Other drugs may undergo chemical changes that produce unwanted side effects (like some antacids which produce cancer-forming chemicals); or grow microbes that can cause serious infections (fungal growth has been a problem with some antibiotics in the past). 

2.     Delay in seeking treatment  

Using medications at home can seem like a quick fix but it takes time to see if they make your pet feel better. This extends the time between illness onset and seeking treatment, causing delays in diagnosis, and increasing the risk of serious complications.  

3.     Ineffective treatment  

We know that expiry dates are set when the medication starts to lose its potency or stability. Administering an ineffective medication means your pet does not receive treatment at all, and this could be life-threatening. For example, using expired tick treatment in a paralysis tick area may result in fatal toxicity. Incorrect antibiotic usage or incomplete courses can also result in relapses and the development of antibiotic resistance.  

4.     Inappropriate treatment  

Treating an illness with the wrong drug can be harmful. Many medicines also clash, causing complicated drug interactions that can prevent your pet from being treated effectively. Changes to your pet’s health or the addition of other medications may mean their previous prescription is no longer appropriate to use. Always check with your veterinary surgeon before giving medications at home.  

5.     Incorrect dosage  

It is common to have medications left over from previous pets who may have passed. When raiding the cabinet for your new pet, remember that most drugs are dosed based on body weight, but this is not the only factor that determines drug dosage. It can be extremely easy to inadvertently give an overdose of medication.  

Common Medicines in the Cabinet 

Prophylaxis  

The most common medications that we might find in the medicine cupboard are preventatives for worms, fleas, and ticks. From the examples above we can understand the risks involved with using expired tablets for life-threatening parasites like paralysis ticks. If the product has passed the expiry date, it is best to discard the rest. The same is also true if the packet encapsulating the tablet or chew has been damaged, as the drug will have been destabilised.  

Ear and eye medications  

Commonly in the form of creams or drops, these drugs are usually used to treat infections.  

Have you ever had to give your dog ear or eye medication? Then you understand how hard it can be to keep the bottle clean! They are very easily contaminated with harmful bacteria which continue to grow in old or inappropriately stored containers. Grabbing an old tube to treat a new infection can mean passing these nasties on to your pet.  

Oral liquids   

Many oral liquids arrive at the clinic in a stable powder form and are reconstituted just before dispensing or are compounded in a special formulation for your pet. These liquids have shorter shelf lives and should not be used after the expiration date. Always check how the medication looks before giving it to your pet. Has it changed colour, become cloudy, or formed lumps? If in doubt, throw it out, even if it is before the expiration date.  

Injectable medication  

Most injectable medications are contained in multi-use vials. The most common example for pet parents would be insulin needed to control diabetes. These drugs can require strict temperature control to prevent bacterial colonisation from occurring during multiple uses. Always adhere to expiration dates and discard the medication if changes occur, or if accidentally left out of the fridge. Remember, the risks are extremely high for diabetics if their medication is not effective.  

Expiry dates on veterinary medicines protect your pet and experimenting with out-of-date medications is a game not worth playing when it comes to the safety of your furry family. 

Key Points to Remember 

  • Expired medications can be unsafe and ineffective. 
  • Using old medicines may delay proper treatment and harm your pet. 
  • Potency, contamination, and incorrect dosing are real concerns. 
  • Never guess dosages or re-use old prescriptions without checking with your vet or SQP. 
  • Dispose of expired or leftover medication safely—ask your vet for advice if you are unsure. 
  • When in doubt, contact your vet early for the best outcome for your pet. 

Always prioritise your pet’s health. If you find old medication at home, do not risk it—speak to your vet for guidance and safe disposal. Early, professional advice is the safest way to care for your furry friend.