Phytotherapy (herbs) for animals: does it work? (Grade C)

What is phytotherapy?

Phytotherapy is the therapeutic use of plant extracts, herbs or plant-based compounds. In animals, it is used for various complaints: liver support, joint complaints, nausea, respiratory infections and gastrointestinal complaints. It is one of the most commonly used forms of complementary veterinary medicine, both by owners and by alternatively-oriented veterinary surgeons.

Unlike registered veterinary medicinal products, herbal preparations are generally sold as supplements in the Netherlands. This has direct consequences for quality control: concentrations, purity and bioavailability vary greatly between products and brands.

Evidence verdict: grade C (weak)

For phytotherapy in animals as a category, evidence grade C applies. This means: there are indications that certain herbs have a biological effect, but well-controlled clinical studies on sufficiently large animal populations are largely lacking. The table below provides an overview of the best-researched herbs.

For milk thistle, the most literature exists: the active ingredient silymarin shows antioxidative and hepatoprotective properties in lab studies, but translated evidence to clinical outcome in sick animals is lacking [1][2]. The RCT on curcumin and Boswellia in dogs with osteoarthritis is promising but too small to be directive [3]. For slippery elm, verifiable clinical research is completely lacking [4][5].

Safety

"Natural" does not automatically mean safe. Herbs contain pharmacologically active substances that can cause damage if applied incorrectly.

Main points of attention:

• Species-specific toxicity. What is harmless for dogs can be toxic for cats, rabbits or birds. Cats lack specific liver enzymes, causing many plant-based compounds to be poorly broken down.
• Quality variation. Herbal products are not pharmaceutically standardised. Concentrations, contaminants and stability differ greatly per product.
• Interactions. Plant-based substances can influence the effect of prescribed medicines — see the interaction list on this page.
• Symptom suppression without diagnosis. Herbs can alleviate complaints while an underlying cause remains untreated. This is particularly risky in severe or progressive conditions.

Legal framework

In the Netherlands, making diagnoses and performing veterinary treatments are legally reserved to veterinary surgeons (Wet dieren [Animals Act], art. 2.11). Herbal preparations are generally brought to market as supplements; as soon as a therapeutic effect is claimed, they fall under the definition of a veterinary medicinal product and registration is mandatory. Owners who apply herbs themselves to sick animals are moving in a grey area — certainly if a recognised condition is present.

Conclusion

Phytotherapy is not a homogeneous category: the scientific basis differs per herb, per animal species and per application. Some herbs — notably silymarin and curcumin — have biologically plausible mechanisms of action and cautiously supportive evidence [1][3], but none of the available studies currently justifies a strong clinical recommendation. Always consult a veterinary surgeon before use, particularly in sick animals, young animals, pregnant animals or animals already receiving medication.