How do I report side effects from my pet’s medication? 

Common Medication Side Effects in Pets 

Symptoms of drug reactions or side effects in pets can depend on several factors: 

• The specific medication and its method of administration. Injectable medications generally carry a higher risk of adverse effects compared to oral medications. 

• The health status and age of the animal. Older pets with pre-existing conditions may respond differently to a medication than young, healthy animals. 

These are some of the most common side effects that pets experience: 

Gastrointestinal Upset  

Mild stomach upset is a common side effect of most pet medications, especially oral ones. Some pets may experience more serious symptoms such as vomiting, diarrhoea, or loss of appetite. These often improve as the pet adapts but can occasionally become severe. Always ask your vet whether the medicine should be given with or without food to help your pet tolerate it better. 

Antibiotic medications commonly cause stomach upset. Consider giving your pet probiotics when they are on antibiotics, to prevent or relieve antibiotic-associated diarrhoea, vomiting, and appetite issues. 

Excessive Salivation 

Some pet medications cause hypersalivation due to their bitter taste. Do not crush these medications, as this can worsen the taste. 

Stomach Ulcers 

Nonsteroidal anti-inflammatory drugs, as well as steroids like prednisone and prednisolone, are known to increase your pet’s risk of getting gastrointestinal ulcers. 

Ulcers can cause vomiting, diarrhoea, and bloody or dark stools. Do not use these medications together, as it increases ulcer risk. Treatment involves acid-reducing drugs and stomach lining protectants. 

While the vast majority of dogs and cats treated with these medications won’t have any problems, if your pet does develop symptoms, get in touch with your vet as soon as you can. 

Lumps and Bumps 

Adverse skin reactions to medications are frequently observed in companion animals. Subcutaneous nodules or swellings commonly occur following injectable drug administration, with a localized lump often appearing at the injection site. Typically, these lumps resolve promptly as the medication is absorbed systemically. 

Skin Irritation 

Oral, injectable, and topical pet medications – including some antibiotics in some pets, thyroid drugs in cats, and flea or tick treatments – may sometimes cause skin irritation in pets. Common symptoms are hair loss, itchiness, swelling, redness, scabbing, bumps, hives, and blisters, ranging from mild to severe and potentially leading to immune issues like lupus. Pets may also lick, bite, or chew irritated areas, worsening their skin condition. 

Liver or Kidney Damage 

Medications for pets are generally processed by the liver and kidneys, which can be very rarely harmed in the process. Side effects may include increased thirst, urination, vomiting, diarrhoea, yellow skin or eyes, and lethargy. NSAIDs may unpredictably cause liver or kidney damage, but proper dosing almost always prevents this. Steroids can also affect the liver, but only usually at very high doses or if the liver is already compromised. Some blood pressure medications may cause kidney problems, but again, usually only if there isn’t enough monitoring. 

Lethargy or Behavioural Changes 

Pet medications can change your pet’s behaviour, either as intended, such as reducing anxiety with sedatives or painkillers like opiates, tramadol, and gabapentin, or as side effects like restlessness or hyperactivity. These changes range from mild to severe and may cause dysphoria, an altered mental state where pets vocalize, pant, or struggle to settle, often seen during or after anaesthesia. 

How can I prevent side effects? 

To help prevent an upset stomach from medication, as owners you can follow these tips: 

• Follow label instructions and give the correct dose on time. 

• Check with your vet before adding new medications, including herbal or natural remedies, as these can interact unpredictably. 

• Give medication only to the prescribed animal. 

• Don’t share doses between pets. 

• Never give dog meds to cats or vice versa – their tolerance for toxicity is very different. 

• Store medication safely and as directed. 

• Tell the vet about past side effects. 

• Inform the vet of health issues and current meds. 

• Ask the vet what to watch for during treatment. 

It’s also important to make sure medication is stored and administered correctly. Good tips to keep in mind include: 

• Store all medications out of reach of children and animals. 

• Store medications in the correct storage conditions according to the label – not too hot, not too cold, not to wet and not too bright! 

• Never use medications that are past their expiry date – at best they won’t work as well, and at worst they could be harmful. 

Who is in charge of side effects? 

The Veterinary Medicines Directorate (VMD) oversees the UK licensing system for animal medicines and manages pharmacovigilance by advising on and processing the reporting of adverse events. Pharmacovigilance aims to identify, understand, and prevent adverse reactions through a strong reporting system. Marketing Authorisation Holders must report any incidents to the VMD within 30 days – this isn’t optional, it an absolute requirement. 

The VMD reviews reports based on severity and possible connection to the medicine, checks for similar cases, and decides if more information or follow-up is necessary. 

My pet has reacted badly to the medicine 

If your pet has suffered any suspected adverse reaction to a licensed medicine, please firstly contact your veterinarian for further advice. It is important that any suspected adverse reactions are reported to the Veterinary Medines Directorate (VMD).  A veterinarian or a Registered Animal Medicines Advisor (RAMA)/Suitably Qualified Person (SQP) are authorised to submit this report on your behalf. 

Either you or your vet can make a report to the MAH (you will find their name on the drug packet, or by looking up the product on the VMD Product Database). They are then under an obligation to pass it on to the VMD. 

If the medicine in question is a human medicine being used in an animal on the Prescribing Cascade, then you or your vet should report it directly to the VMD using the links below. 

How common are adverse reactions? 

Thankfully, adverse events such as harmful, unexpected side-effects to animal medicines are extremely uncommon. Before any animal medicine is allowed onto the UK market it has, by law, to satisfy very strict criteria on its quality, its effectiveness and its safety. However, once an animal medicine is in use, it is vital to know if any animals or people suffer unexpected problems following use or exposure to the product under field conditions. 

Very occasionally animals may have a reaction following use of a medicine. If you are an animal owner and your animal is unwell after treatment with an animal medicine or if you are at all worried, contact your vet. 

The VMD use a standard classification system for how common adverse effects are:

• Common: More than 1 animal per 100 treated
• Uncommon: 1-10/1000
• Rare: 1-10/10,000
• Very rare: Less than 1/10,000

For any licensed medication, you can look up how common its side effects are on the VMD Product Database.

What happens after a report is made? 

The Veterinary Medicines Directorate (VMD), which administers the licensing system for animal medicines, is responsible for pharmacovigilance in the UK, giving advice on reporting adverse events linked to the use of animal medicines. The purpose of pharmacovigilance is to detect, understand and prevent adverse events, and this is built on robust reporting system, to monitor any and evaluate the reported adverse events. Marketing Authorisation Holders are legally obliged to advise the VMD of any reports they receive. 

Reports received by the VMD are prioritised in terms of severity and likely causality (i.e. to see whether the problem is likely to be linked to the medicine). They also analyse whether there have been any other reports about the same product or others like it, whether any further information is required and whether any follow-up is required. 

Once reports are received, the VMD prioritises them based on the severity of the incident and the likelihood that it is linked to the medicine in question. They also look for similar reports involving the same or related products, assess whether additional information is needed, and determine if any further action or investigation is required. 

In the most extreme cases, there may be a product recall, if very severe problems are being seen across a lot of animals. This is very rare, as common and severe problems should be caught in the pre-authorisation testing phase, but it does occasionally happen. More commonly, there may be a batch recall, where one batch of the product is recalled due to a manufacturing problem. 

In other situations, it’s more likely that, if a new side effect or risk factor is identified, it will be added to the product’s Summary of Product Characteristics (the legal document that tells vets and owners what to expect). This would be the case if the side effect is uncommon in that most pets do not experience it, but common enough that it can be causally linked to the drug – for example, one dog arthritis treatment had a less than 1:1000 risk of wobbliness after injection added to its datasheet earlier this year. 

Ultimately, the VMD, manufacturer, and your vet all want the medicines we use to be as safe as possible. As a result, reporting side effects is something we should all be doing, to help us gather that information. 

Further Reading and Useful Links 

Report a Veterinary Medicine Problem – VMD  

Guideline III: Adverse Event Reporting – UK Government  

Adverse Events – VMD Connect 

Pharmacovigilance of Veterinary Medicinal Products in Great Britain – UK Government