herbal medicine safety



It’s frustrating, as a vet who has undertaken extensive training in physiology, conventional pharmacology, and then studied herbal pharmacology on top, to read the advice of all the ‘experts’ on the internet. Today, a post popped up on my Facebook feed all about the benefits of turmeric which included this gem, “I take it three times a day. It’s natural, what harm can it do?”

The answer is that if there are chemicals present in a herb that can do good, there is also the potential for harm.

Obviously, some herbs are well known for their toxicity. Although foxgloves and lily of the valley contain chemicals that can be used to treat heart disease, we don’t use them because the risk of poisoning and death is too high. But there are many herbs that we do use that can be therapeutic at one dose, but poisonous at a higher dose. A good example would be garlic; small doses can be very useful, but even moderate doses over the long term can cause blood disorders in some animals, especially cats. Some herbs can irritate the nose, mouth, or gut if given in large quantities, or if not mixed well into food.

Whilst we’re on cats, they are very tricky creatures! There are differences in how cats metabolise drugs…and herbs…which make them far more toxic than they are to humans or dogs. Worryingly several herbal preparations are sold over the counter for arthritis in dogs and cats which contain willow bark. Willow bark contains compounds similar to aspirin which can be toxic to cats if given in even moderate doses over a period of time. And although nobody is suggesting lilies as a botanical medicine, these pretty plants can prove fatal to cats if they ingest even a small amount of pollen.

Next comes the problem of giving herbal medicines without your vet’s knowledge when your pet is on medication. Almost everything taken into the body, drug, food, or herb, will be metabolised. Much of this metabolism happens in the liver, where a limited number of enzymes get to work on a huge variety of natural and artificial compounds. Some compounds compete for the same enzyme which slows down their metabolism. Other compounds may slow down or speed up the activity of an enzyme which metabolises another drug. Turmeric has many of its anti-inflammatory and anti-cancer effects through inhibiting enzyme reactions…but this also means it could slow down the metabolism of other drugs. This may be a benefit, leading to a greater effect, but could also lead to toxicity. St John’s Wort is well known for increasing the activity of certain enzymes, meaning other drugs are cleared more quickly from the body. In humans progesterone in contraceptive pills is a concern, but in animals clearing antibiotics too quickly would be a concern. St John’s Wort also works to reduce the reuptake of serotonin and dopamine in the brain, hence its usefulness for depression in humans. But if given with other medications (especially antidepressants) which also block neurotransmitter reuptake there is a high risk of side effects, including the sometimes fatal serotonin syndrome. And it’s not just herbal medicines; broccoli and sprouts can increase specific enzyme activity, and grapefruit can inhibit enzymes.

Finally, I am always concerned about the quality and safety of herbal medicines. Even where a particular herb is safe, and should be effective, buying the right tablet or tincture is essential. Very few companies make herbal medicines with the attention to detail that they should and this can lead to ineffective, or unsafe products. Research done by the BBC last year found that most over the counter herbal products contained little active ingredient. Some contained no active ingredients, and some…unknown compounds. Herbs may be incorrectly identified before processing, poorly stored, or have grown in poor conditions meaning they contain less active compounds. With dried ground herbs, such as turmeric, the method of drying and grinding can significantly affect quality, and where a herb contains essential oils, drying can remove many of these.

At Four Seasons Holistic Veterinary Care we love herbal medicines. But we strongly believe they should only be used after consultation with a vet who is trained in their use. In addition we only use herbs from companies which perform sufficient quality control.




The internet is an amazing place…so much information, and so easy to buy anything at the click of a button. But it has it’s dangers.

Imagine your dog is due for worming…you usually get some stuff from the vet but it’s quite expensive and you aren’t heading in to town so you look online. First you find your usual wormer available from an internet pharmacy. You check the pharmacy is properly registered in the UK, and that you don’t need a prescription, and you’re just about to pay when….

You notice an article saying how bad chemical wormers are for pets. You read it and it’s scary stuff! One dog died, another had fits. So now you start looking for a more natural approach…something herbal. There are lots to choose from and they are all quite cheap, come with glowing testimonials and there is no mention of side effects. Great! Let’s order some….

Or maybe your cat has been diagnosed with cancer and the vet says there is nothing that can be done other than supportive care…but a quick internet search reveals several herbal tonics with great reviews…


Before you put in your credit card details have a really good look at the products. The manufacturer should be able to tell you what herbs are in the product, at what strength. They should be talking about amounts of active chemicals, not just how much dry or fresh herb was used as herbs can vary in strength from season to season. Can the producer tell you how they quality check the herbs and where the herbs come from? Many herbs are rare in the wild and must be farmers of collected under strict controls, other herbs look similar to plants which are toxic or have no medicinal actions. Has the product been tested to show it is safe and effective? Beware of simple testimonials; “I use ‘herbal worm prevent’ on my dog and he never has worm!” may be true…but as most worm infestations aren’t obvious without faecal testing can the owner really be sure? For a worming product we would expect to see a study where pets were tested for worm eggs before treatment and split into a control group (no treatment) and a treated group, then tested again. Similar tests can easily be done to show the effectiveness of flea products. Cancer treatments are more difficult for a small herbal company to test and though most will do no harm, they may also do little good. Cancers can be very variable in how they affect pets. Some grow slowly and some grow fast even if you do nothing at all. Many herbs have well known side effects, especially at higher doses- does the company mention these, or any interactions with conventional drugs (there are many!).


We don’t offer miracle cures. We prefer monitoring for parasites and using appropriate doses of licenced products when required. These products can have side effects, but they are uncommon and well known and we take them into account when weighing up which products to use.

We do offer bespoke herbal medicines to support pets with a huge range of medical conditions, but our training means we are well aware of potential side-effects, drug interactions etc. We only buy herbs from manufacturers who follow Good Manufacturing Practice, and source herbs in an ethical and sustainable way.

So….instead of buying a miracle potion….book a consultation with us!