How Your Pet’s Drugs Interact with Herbs and SupplementsDrugs can alter the potency of herbs and supplements, can cause side effects
Millions of pets are given drugs that can interact with the way their herbs and supplements are metabolized by their bodies.
Nancy Scanlan, DVM
As million of Americans give their pets prescription drugs in an effort to overcome problems and help them live a longer life, there is increasing evidence that these drugs can interfere with a wide variety of herbs and supplements used to help everything from cancer to separation anxiety to high blood pressure.
Recent studies have found that a great number of drugs may affect the way certain enzymes in the body metabolize supplements. Some drugs may inhibit the enzymes’ ability to break down a supplement and clear it from the body, causing supplements or herbal ingredients to build up to potentially toxic levels and even cause overdose. Other drugs may increase the rate at which a supplement is broken down, clearing it from the body too quickly to be effective.
As an increasing number of drugs are approved for use in animals, researchers are studying the interactions and side effects prescription drugs have on herbs and supplements recommended and prescribed by holistic veterinarians.
Drugs, for example, can interfere with herb and supplement-metabolyzing enzymes in the liver, stomach and intestines and proteins in the blood that can alter the way herbal products and supplements are distributed throughout the body.
Researchers at the University of Minnesota in Minneapolis are exploring interactions between cancer drugs and dietary supplements, based on data extracted from 23 million scientific publications (mostly concerning humans), according to Rui Zhang, a clinical assistant professor in health informatics. In a study published last year by a conference of the American Medical Informatics Association, he says, they identified some that were previously unknown.
For example, the herb Echinacea, shown by research to be effective in respiratory disease as well as increasing the number and activity of cells in the immune system, is also known to affect the way certain chemotherapy drugs work. By boosting their effect, lower doses can be taken, reducing the cost of chemotherapy for pet owners.
Philip Gregory, an associate professor of pharmacy and director of the Center for Drug Information and Evidence-Based Practice at Creighton University in Omaha, Neb., notes that the FDA has given warning letters to makers of herbal products for humans, usually for adding drugs. This is almost always for products for weight loss or body building. Supplements for animals which carry the NASC seal do not have this problem, since the company must submit certificates of analysis for each of their products in order to be eligible for this seal. Animal herb and supplement products are superior to most produced for humans, in this respect. They are also required to submit reports on adverse events associated with their products, allowing oversight of the industry for potential side effects, including drug interactions. In contrast, drug manufacturers are not required to report interactions with herbs and supplements.
The National Center for Complementary and Integrative Health, part of the National Institutes of Health, is funding a number of programs around the country to study potential adverse interactions that can occur between herbs, supplements, and prescription drugs, over-the-counter drugs such as aspirin and even small molecules in food. The risks are especially high for cancer and surgery patients and those on heart and blood-thinner medications, which have what’s known as a “narrow therapeutic range,” or small differences between beneficial and toxic doses. This is another reason to get pets off those drugs and on to herbs and supplements with a much broader therapeutic range.
Prescription medications can also interfere with each other, but the Food and Drug Administration requires drug companies to disclose information on potential interactions as part of its drug approval process. There is a 650-page report published each year for this information. In spite of this, there are over 2 million adverse drug reactions each year and 100,000 drug-related deaths each year in humans.
More than half of human patients with chronic diseases or cancer use herbs and dietary supplements and many take them at the same time as prescription medication, studies have found. A similar pattern is true of pet owners and their pets.
“Our greatest concern is making pet owners aware that some of these herbs can decrease the dose needed for chemotherapy drugs,” says a holistic veterinarian who wishes to remain anonymous. For more information owners can go to a Sloan Kettering website, About Herbs, and an app veterinarians and petr owners can use to search for potential interactions between dietary supplements and prescription drugs.
Used in small quantities, such as in cooking, herbs are generally safe, Dr. K. Simon Yeung, a doctor of pharmacy and herbalist at Memorial Sloan Kettering Cancer Center in New York, notes. But when concentrated in pills and capsules and taken in large amounts over time, they can have medicinal effects, so pet owners should consult a holistic veterinarian trained in their use.
Malcolm Taw, director of the UCLA Center for East-West Medicine-Westlake Village in Los Angeles, recommends that instead of taking supplements, people should eat foods rich in certain compounds that have potential benefits. For example, lab studies have suggested a natural compound, quercetin, has cancer-fighting properties, and combined with green tea could help make a chemotherapy drug used in prostate cancer more effective. But in supplement form, quercetin can also potentially interfere with medications including antibiotics, and animal studies are lacking. Dr. Taw suggests eating more apples and onions, which contain quercetin. Of course Dr. Taw is not a veterinarian and obviously does not know about bad effects of onions in dogs.
With funding from the NIH, researchers at the UIC/NIH Center for Botanical Dietary Supplements at the University of Illinois in Chicago plans to start the first of three human trials in July to explore how the supplements may interact with prescription medications women take for other health issues such as high blood pressure and cholesterol. This can give valuable information about their use in animals.
In a review published in the February issue of the journal Drug Metabolism and Distribution, Dr. van Breemen and Alyssa Sprouse, program manager at the University of Illinois research center, found that clinical studies of some botanicals, such as milk thistle, that were predicted to interact with drugs were found not to be problematic. Although physicians believe this may be in part because the body didn’t absorb the supplement in large enough quantities to affect a drug’s metabolism, as Dr. Sprouse says, they obviously are judging harmless herbs by the never-harmless standards of drugs. Veterinarians who have studied botanical medicine know which herbs can be used with minimal problems.
To avoid expensive trials in humans of substances that show no adverse effects, the University of Illinois team is using mathematical models to help identify which predicted drug-supplement interactions warrant study in humans.
Ryan Terlecki, director of the men’s health clinic at Wake Forest Baptist Health in Winston-Salem N.C. says some of his prostate cancer patients take supplements to deal with side effects of treatment and to prevent recurrence. He says he respects their desire to try something natural, but he also advises them that “when you are trying for a cure, you don’t want anything that is going to inhibit that.” He should probably look into Chinese herbal medicine for this problem, and decrease drugs that would interfere with those herbal formulas.