Why supplements aren’t medicines, and can’t replace your pet’s prescription 

You’ve come out of the consulting room with a diagnosis, a prescription, and a lot of unanswered questions. Your vet seemed confident, but busy, so you nodded along. Now you’re worried. Is this medicine really safe for your pet? What if it makes things worse? And is there something gentler you should be trying first?

Worried about giving your pet prescribed medicine? 

You read the enclosed leaflet, also called the data sheet. It lists everything that might go wrong, from vomiting or lethargy to, rarely, something much worse, and it’s hard not to read it as if it were all about your pet. Then you search online, and the first people to answer are often selling an alternative: a photo of a happy dog in a field, and the word “natural” across the front of the tub. 

That’s very tempting, because it promises what you want most, a way to help your pet with no risk at all. However, that is a false comparison. Giving the medicine has risks, and the leaflet tells you what they are. Leaving the condition untreated or using an ineffective product has very real risks of its own, and these are not written down anywhere. Without effective treatment, conditions progress, and painful conditions affect your pet’s wellbeing. I call pain a “welfare blocker”, because a pet in pain can’t fully enjoy and engage with positive life experiences.  

Worrying is a natural reaction when you are dealing with a new diagnosis or a change in the plan. The important thing is to seek to understand the genuine risk vs benefit in your pet’s own unique situation.  

How to read your pet’s medicine data sheet without panicking 

The data sheet for an authorised veterinary medicine is formally called the Summary of Product Characteristics. Its section on adverse events lists what has been reported after the medicine was given. The list is there so you and your vet know what to watch for, not to predict what will happen to your pet. 

How long the list is matters less than how often each thing happens. The regulator for veterinary medicines, the Veterinary Medicines Directorate (VMD), uses internationally agreed wording [1]: 

So a sign described as “very rare” might rest on a single report. It might not even be a true side effect. The VMD says that something happening after a medicine is given doesn’t necessarily mean the medicine caused it [1]. People are asked to report anything they suspect, even if they can’t prove a link, and sometimes the signs come from the condition being treated, not the treatment. 

A long list looks alarming, but it doesn’t mean the medicine is more dangerous. It means problems are being recorded. Data sheets are updated as new monitoring information comes in, so that vets and owners get to know about it. A supplement tub that lists no side effects hasn’t been proven safe. It just hasn’t been through that scrutiny, so the silence tells you nothing. 

When you read a data sheet, look for four things: how common each effect is, how serious it is, what you should watch for at home, and which animals shouldn’t have the medicine. 

Are prescribed medicines safe for pets? Risk versus benefit 

Medicines generally work by deliberately interfering with body processes that have gone wrong. That interference is sometimes where the risk comes from, because the same process often does other jobs elsewhere in the body, and that is often where side effects arise. A treatment with no risk of side effects may be one that has no effect at all, which is worth remembering whenever a product promises “no side effects”. It’s why your vet thinks about your pet’s age, other conditions and other medicines before choosing one, and why some come with monitoring.  

When thinking about medication risks, I would always ask the question “how do the medicine’s risks compare with the alternative”, rather than just “is this drug safe”. A rare, manageable side effect can be a much smaller problem than months of pain, or a condition left to progress. 

Some helpful questions to ask your vet: 

• What is this for, and what happens if we wait? 

• How likely, and how serious, are the side effects in a pet like mine? 

• What should I watch for at home, and when should I ring you? 

• What monitoring will we do? 

• If it doesn’t suit my pet, what are the alternatives? 

• When will we review whether it’s working? 

Pet supplements or medicines: what’s the difference? 

In UK law, a medicine is anything that treats or prevents disease, or changes how the body works – or which claims that it does [2, 3]. Before a medicine can be sold it has to be authorised, which means the regulator has checked that it is safe, well-made and that it works. 

Supplements are classed as feed. They are checked for safety and labelling, but they don’t have to prove they work, and they are not allowed to claim that they do. “Natural” or herbal makes no difference. If a product is sold to treat or prevent disease, it is legally a medicine, however natural it is [2]. 

What can pet supplements legally say? 

The rule is simple. A supplement can be sold to help maintain health in a healthy pet, and nothing more [2, 3]. 

Allowed 

• Saying the product helps maintain general function in a healthy pet, e.g. “supports digestion”, “maintains joint health” 

Not allowed 

• Claiming to treat, cure or relieve a disease 

• Claiming to prevent a health problem developing 

• Naming a condition such as arthritis, allergy or diarrhoea, or using medical words like “dose”, “treatment” or “relief” [3] 

• Using testimonials or before-and-after photos that show relief of a condition 

So if a supplement is being sold for your pet’s diagnosed condition, either it is an unauthorised medicine or it is making a claim it shouldn’t. Neither is reassuring. The same rules cover social media posts, which count as advertising [2]. If you see these kinds of claims, you can report them to the VMD.

Pet influencers, guilt and unproven claims 

These limits apply to influencers too, but there are still many stories online about miracle reactions to products. One person’s story can’t show whether a product works. 

Then there’s the pressure. I’ve seen owners who choose a prescribed medicine told in comment threads that they’re poisoning their pet, while the remedy being promoted is sold by the person making the accusation. Guilt sells well, because it makes a medical choice feel like a verdict on you as an owner. This is doubly risky. Owners may stop telling their vet what they’re giving, which means they no longer have the full picture, and owners who feel ashamed may delay or give up treatment that was working. 

A fair test for any post, video or group is to ask: who is telling me this, what do they gain if I act on it, could they say it on the product label, and are they trying to shame me for following my vet’s advice? If a claim about disease couldn’t legally appear on the packet, be cautious. 

Do pet supplements work? What the research shows 

In spite of all I have said above, I am not saying that supplements are all a waste of time. For many, we simply do not know because studies have not been done. Often the studies that have been done are small and that limits the conclusions that can be drawn. Table 1 shows where we are with the evidence behind some products. 

Table 1: What we know so far about some supplements 

Turmeric for dogs: does it work? 

Turmeric is a good example of an idea that is not backed up by evidence. It is marketed everywhere, it feels safe and wholesome, and the idea that it is anti-inflammatory is reasonable, because its active ingredient, curcumin, has anti-inflammatory effects in laboratory studies. However, curcumin is poorly absorbed when swallowed [15]. A review of the laboratory evidence, published in a journal focused on traditional Chinese veterinary medicine rather than conventional veterinary science, included no studies in dogs [15]. 

The evidence in dogs is very thin. In one placebo-controlled trial of 42 dogs with arthritis, a diet containing turmeric extract (alongside collagen and green tea extract) was linked with better owner-reported pain scores. However, force-plate measurements, which record how much weight a dog puts through a leg, showed no significant difference [16]. The force-plate measurements are the data that matters, because we know owner observations may not be accurate (see later). The trial was small and funded by the diet’s manufacturer, and because turmeric was only one ingredient, it can’t tell us what turmeric alone does. It is not proven, and it is no reason to stop pain relief that is working. 

Does the tub contain what the label says? 

Even a good ingredient only helps if it’s in the tub. In one US test in 2009 of animal joint supplements, four of the six lacked the amount of glucosamine or chondroitin stated on the label [17]. Trial results for one product also can’t be assumed to apply to another, because formulations differ. This is a reason to stick with reputable brands when using supplements. 

It’s hard to tell by eye whether a supplement is working, too, because of the caregiver placebo effect. In a placebo-controlled trial, around four in ten owners reported improvement in dogs that had only been given a dummy treatment [18]. That’s not carelessness or a lack of love. Hope simply colours what we see. So “my dog seems brighter since we started it” isn’t proof the product works. 

The real risk of unproven remedies is lost time 

The biggest welfare risk of an unproven remedy is rarely that it directly harms the animal. More often it takes the place of treatment that would have helped. Arthritis, for example, is chronic and painful, and every month spent waiting for a supplement to “kick in” is another month of pain and lost mobility for your pet. 

Products marketed for “calm” or “digestive balance” can delay the investigation of a pet whose behaviour, appetite or stool has changed for a medical reason. Get the diagnosis before you buy the supplement, because it tells you whether a supplement is even the right sort of product. 

Money matters too. A cupboard full of products with weak evidence can use up the budget that would have paid for a medicine with proven benefit. If funds are limited, they should go first on whatever has been shown to work. 

There are also wider environmental harms in manufacturing, transporting and selling products with no proven benefit, especially if that product comes from oceans or contains products derived from other living beings.  

Are pet supplements worth buying? Six questions to ask first 

Supplements can be a reasonable add-on, alongside a confirmed diagnosis and an effective treatment plan. Before you buy, it helps to ask: 

1. Has a vet confirmed what is wrong? What is their view on the supplement? The product should support a plan, not stand in for one. 

2. Does the label stay within what’s allowed? A product that names your pet’s disease is making a claim it isn’t permitted to make – which makes the product far more suspect, as if they are ignoring medicines law, what else are the manufacturers doing, or not? 

3. Is there a trial in dogs or cats, using this ingredient at this dose, with an objective outcome rather than owner opinion alone? 

4. Does the label state the amount of each active ingredient, and is there evidence that the contents are tested? 

5. What will we measure, and when will we review? Agree a point with your vet to stop if there’s no clear benefit. 

6. Does it affect anything else your pet takes? Tell your vet about every product, however natural. 

In summary 

A supplement with modest evidence can sit comfortably alongside effective treatment. It should never be the reason effective treatment is delayed. 

Avoid products with claims that appear to be too good to be true, are not aligned with the law and come with a side dose of shaming or guilt. 

Finally 

I’m not a cheerleader for the pharmaceutical companies, and I don’t receive any benefits of any kind from them. I don’t like how some of them have behaved around the licensing of generic human medicines that vets have used for years, and I always look carefully at their claims and their science, which can also sometimes be poorly designed. So asking questions is right. Avoiding medicines that help is not. 

I’m Dr Caroline Allen FRCVS, a vet and former RSPCA Chief Veterinary Officer, and the founder of Pet Lighthouse, an independent veterinary consultation service www.petlighthouse.co.uk. 

If you’re weighing up your pet’s medication, supplements or treatment options and want a clear, unhurried second opinion, I offer online consultations across the UK, and in-home assessments in London. I don’t prescribe medicines, sell products, or earn anything from what I recommend, so my only focus is your pet’s comfort and quality of life.  

You can book a free ten-minute introductory chat here: https://petlighthouse.co.uk/introductory-chat   

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