Drugs and dietary supplements for dogs: What’s the difference?

Using science to make informed choices

As a veterinarian, my job is to help my patients live the longest, healthiest life possible, and to help my clients choose among different treatment options for their pets. When I consider recommending a medicine for my patients, one of the most important things I need to know is how good the scientific evidence is showing that medicine is safe and effective. A really useful resource to help me determine this is whether or not that treatment has been approved for use in dogs by the FDA.

FDA categories help vets distinguish the evidence available for a product

There are different categories of medicines to choose from, and different degrees of regulatory oversight for each, and this can make understanding the strength of the science behind specific treatments a lot easier. 

In general, vets can choose among medicines in several broad categories:

1. Prescription drugs fully approved under the supervision of the Food and Drug Administration’s Center for Veterinary Medicine (the FDA CVM)*

2. Prescription drugs conditionally approved under a formal FDA process

3. Drugs approved for use in humans or other species and used “off-label”† in dogs

4. Dietary supplements or other non-prescription treatments not tested or approved under a specific regulatory process

Some treatments are available “over-the-counter,” meaning they have met the same testing requirements as prescription products, but they can be safely and effectively used without supervision by a veterinarian.

How these categories fulfill the needs of our pets

In general, the strength of the evidence identifying both the benefits and the risks of these treatments is greater the closer to the top of the list they are. For example, it takes a lot more research and data in dogs to achieve FDA approval for a prescription medication to be used in dogs than is required for a human drug used off-label or for a dietary supplement. 

Fully approved prescription drugs

The highest bar for scientific evidence is set by full FDA drug approval. This is a complex process that requires demonstrating to the agency that a drug proposed for use in dogs is safe, for the dogs taking it as well as for the humans around them, and that it is effective, meaning it consistently does what it’s expected to do. Full approval requires showing that a drug can be consistently made to a high standard of quality. 

Of course, no scientific or regulatory process is ever perfect. However, the standard of FDA approval is rigorous, and as a vet I know that an approved prescription drug has been tested extensively and has more scientific evidence to support safety and efficacy than any other category of treatment I could use. 

Conditionally approved prescription drugs

The expanded conditional approval process is a relatively new category which recognizes that for conditions that are serious and have no existing effective treatments, a process that makes new drugs available for vets and dog owners to use sooner is beneficial. 

→ See our previous blog post explaining conditional approval in more detail

Conditional approval requires nearly all of the same conditions to be met, such as proving safety, manufacturing quality, and so on. The only difference from full approval is the type of proof of effectiveness. Rather than meeting the “substantial evidence” for effectiveness standard, which typically requires a clinical trial in companion dogs, conditional approval requires meeting the standard of a “reasonable expectation of effectiveness” (RXE). This standard can potentially be met with studies that involve fewer dogs and shorter time periods than the clinical trials needed for full approval or with evidence already existing in the scientific literature from studies done in the past. 

→ See our previous post announcing the FDA acceptance of RXE for one of our own products

Off-label use of drugs

Many more drugs are approved and available for use in humans than in dogs because the biomedical industry for humans is much larger and better funded than veterinary medicine. The FDA recognizes that many potentially beneficial drugs are available in people, or other species, that will never be put through the approval process for use in dogs due to limitations of time, money, or other factors. Since 1994, the agency has allowed vets to use these drugs under specific conditions, and this is known as “extra-label” or “off-label” use.

Extra-label use of drugs approved for humans is one of the most common types of medication used in veterinary medicine. Vets understand that the evidence for safety and effectiveness in our patients is not as strong as it is for approved animal drugs, but these drugs are an indispensable tool in caring for our patients.

As long as we, and our clients, understand the limits of the evidence, we can balance risks, benefits and uncertainty in a rational way and monitor patients appropriately to make sure we are truly helping them.

Supplements

Dietary supplements are the category with the least oversight and the greatest uncertainty about safety and efficacy. In veterinary medicine, this is not even a formal category. As the FDA explains, “there is no ‘dietary supplement’ regulatory classification for animal food substances and products. They are considered either ‘foods’ or ‘new animal drugs’ depending on the intended use.” 

Essentially, anything that is intended to cure, treat, or prevent disease is considered a drug and should, in principle, go through the full or conditional approval process before being marketed for use in dogs. In practice, though, the FDA does not aggressively enforce this policy.

Why a lack of evidence in supplements matters

As a vet, the importance of this to me is that supplements for pets aren’t required to prove they are safe and effective before, or after, being marketed. Most of these products have never been tested in clinical trials.

There is also no official regulatory monitoring of quality for most dietary supplements. One study found, for example, that the labels for many probiotic supplements were inaccurate—often the product didn’t have in it what the label said was in it. Even if a specific supplement might have therapeutic effects, your dog won’t benefit from these if the product you buy doesn’t actually contain the ingredients it’s supposed to have!

I do sometimes recommend dietary supplements if there is some scientific reason to believe they might help and are unlikely to be harmful, but my confidence in these products is much lower than for prescription drugs.

The bottom line

There is always some level of risk in doing anything in medicine, and this has to be balanced against the benefits of what we are considering doing. In a dog who is seriously ill, a medicine that can cure them or greatly relieve their suffering has a lot of potential benefit. The risk of some side effects may well be worth taking in such a case. For a healthy dog in whom we are aiming to prevent illness down the road, we would be a lot less likely to take any significant risks at all with our preventive treatments.

However, as a vet and as a dog owner myself, I can only decide what is best for my patients and my pets if I know what the potential risks and benefits are for the medicines I have available. The levels of regulatory oversight I have described can help a lot in understanding the strength of the scientific evidence and the degree of confidence I can have in the medicines I recommend.

Whenever possible, I will always choose those treatments that have the highest degree of evidence behind them because this gives me the greatest chance of helping the dogs I care for. 

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^*Some veterinary products are regulated by other agencies, such as certain parasite preventatives (EPA) and vaccines (USDA), but FDA is responsible for approving most prescription drugs.

^†”off- label” is a common term vets use to describe what the FDA more often calls “extra-label” drug use.