“There is no evidence that it works” is a frustrating phrase that we commonly hear as veterinary herbalists. We suspect what is actually being said is that there are no large-scale clinical trials that are species-specific for our patients. This is, indeed, true, as it is with many therapies and treatments in our industry. So, in this article, we aim to explore what “evidence-based” means and what good evidence is available for the use of plant-based medicine.
Evidence-based medicine
In evidence-based medicine, various types of studies contribute to understanding the effectiveness and safety of treatments. Clinical observation and case reports provide anecdotal evidence but are susceptible to bias and confounding factors. That said, all medical progress starts here. Cohort studies are next on the list, again leaving us with an impression of evidence but still lacking statistical relevance. This is where we, as an industry, like to see randomised controlled trials (RCTs), which are considered the gold standard for evaluating medical interventions. They involve randomly assigning participants to treatment and control groups, thus minimising bias and providing stronger evidence of causality. Blinding participants and clinicians where possible reduces the risk of bias even further.
Unfortunately, many of the RCTs we have in the veterinary field have low numbers (sample size, values, etc) which makes them less statistically relevant. A way to help improve statistical relevance is to use meta-analysis and systematic reviews. These are comprehensive analyses of existing research. The data and results from several studies are combined to enhance the power and precision of findings.
When we are looking for evidence for herbal and plant-based medicine, it isn’t always found in the easiest of places, but it is there!
Obtaining high-quality trials for herbal medicine presents several challenges. Firstly, standardisation of the products can be difficult due to variations in growing conditions, plant species and preparation methods, which can lead to inconsistencies in dosing and formulations. Additionally, herbal medicine often involves complex mixtures of compounds. Many studies focus on isolating one specific active ingredient without considering the synergistic effects of all the phytochemicals when used together. This complexity poses challenges in designing appropriate control groups and blinding procedures. Regulatory hurdles and the high cost of conducting large-scale trials also contribute to the scarcity of high-quality research in herbal medicine.
So, when we are looking for evidence for herbal and plant-based medicine, it isn’t always found in the easiest of places, but it is there! We have put together some of the evidence base available for various plants and their uses. Clearly, this is a very broad topic, so we have selected a handful of studies as examples.
Crataegus monogyna – hawthorn
Traditionally, hawthorn is known as the “father of the heart”; it has been used for general heart health, managing blood pressure, supporting cardiovascular function and improving circulation. Many of these effects are attributed to its high antioxidant levels.
Guo et al. (2008) looked at 14 trials that used hawthorn as an adjunct to conventional therapies. This review concluded that “there is a significant benefit in symptom control and physiologic outcomes from hawthorn extract as an adjunctive treatment for chronic heart failure”. The degree of positive outcomes and lack of side effects suggests this treatment should be considered for most chronic heart failure patients. While these studies were conducted on humans, the wide safety margins mean extrapolating its use for veterinary medicine is reasonable.
Hypericum perforatum – St John’s wort
St John’s wort is a herb that has been used for many years in many capacities, namely for the treatment of depression and other mental health issues. The anecdotal evidence in mental health has sparked a large number of trials, making this one of the most rigorously studied plants in relation to medicine.
A systematic review by Linde et al. (2008) concluded: “The available evidence suggests that the hypericum extracts tested in the included trials a) are superior to placebo in patients with major depression; b) are similarly effective as standard antidepressants; c) and have fewer side effects than standard antidepressants. The association of country of origin and precision with effects sizes complicates the interpretation.” This is one of many systematic reviews and RCTs that look favourably on the use of St. John’s wort for depression and other mental health concerns.
Silybum marianum – milk thistle
Milk thistle is commonly used (in various forms) in veterinary practice, but many do not know the research behind it. The most common use of milk thistle is for hepatoprotection and support, and for good reason.
The veterinary interest in this herb began with a study from 1984 which looked at the hepatoprotective effects of silibinin, one of the active phytochemicals found in milk thistle (Vogel et al., 1984). Since then, there have been many studies to support its use in treating liver disease and fibrosis, including studies in canine patients.
In 2012, the Journal of Veterinary Internal Medicine published a literature review of the evidence, both human and veterinary, for the use of milk thistle in medical practice. This review summarised much of the evidence for the use of the herb in practice (Hackett et al., 2012):
- “Silibinin also has been shown to be protective against radiation-induced hepatic injury and increases in hepatic enzyme activity, as well as that induced by doxorubicin”
- “Double-blinded placebo-controlled studies have demonstrated significant decreases or normalization of hepatic enzyme activity in alcoholic liver disease, as well as improvement in symptoms of anorexia, nausea, and asthenia. Improvement in histological scores of hepatic pathology have also been observed in these patients”
- “The incidence of complicating conditions such as hepatocellular carcinoma, upper gastrointestinal bleeding, and diabetes mellitus also was lower in silibinin treated patients”
Curcuma longa – turmeric
There is no doubt that at some point in your career, you have been asked by a client about whether they should use turmeric for various conditions, usually osteoarthritis. There have been numerous studies looking at the anti-inflammatory, antioxidant and hepatic effects of turmeric. Many of these are positive and are worth considering, particularly where conventional treatments are not an option: for example, a patient with osteoarthritis suffering gastrointestinal effects from non-steroidal anti-inflammatories (NSAIDs) – a contraindication for the usual treatment method.
In their systematic review, Wang et al. (2021) found that: “Turmeric extract is a safe and effective option for the symptomatic management of knee [osteoarthritis], compared to placebo or NSAIDs.” This review also discussed the concern that short-term and heterogenous studies may affect bias – a common issue in many smaller-scale studies – and noted the lack of side effects associated with the use of turmeric in these trials. Other studies also suggest that turmeric is beneficial for arthritic pain and for the treatment of gastric ulcers (Rafatullah et al., 1990); these two effects are undeniably useful to many of our patients.
Mentha piperita – peppermint
It is not uncommon for people to use peppermint to aid digestion and tackle gastrointestinal discomfort or gas; this is for good reason.
Khanna et al. (2014) found in their systematic review that: “Peppermint oil is a safe and effective short-term treatment for IBS [irritable bowel syndrome].” However, it is important to note that this study was conducted in humans, using peppermint oil. In animals, we are much more cautious about using oils, particularly in cats because they are very sensitive to volatile oils. That said, administering peppermint tea to dogs with mild gastrointestinal disturbances is very safe and effective.
Conclusion
These are just a very small handful of studies looking at the positive effects that herbal medicine can have on patients. But you may notice that some of the reviews comment on bias and methodology of the trials; this is not uncommon with systematic reviews and is symptomatic of the bigger issue of funding large-scale trials.
Regardless, these studies all look positive or, at the very least, promising. They also show little to no concern about potential side effects in comparison to veterinary pharmaceuticals. If we have the ability to aid and improve our patients’ outcome measures and quality of life with few to no adverse effects, why wouldn’t we use plant-based medicine as an adjunct to conventional treatments? To say there is no evidence is inaccurate; we just need to know where to look!
