herb toxicity

HERBAL MEDICINE SAFETY

IT’S NATURAL, SO WHAT HARM CAN IT DO?

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.