Herbal Medicine Safety: What Every Beginner Should Know
If something is natural - does it automatically mean it's safe?
A fellow Threads user asked me to cover herbal safety (you can follow me there: @thebuffaloherbalist, I post a lot of herbal tips and facts!). They specifically asked about herb-drug interactions, but I knew I wanted to take it a step further. This article is jam-packed with info, so come back to it if you need.
I want to debunk the myth that just because something is natural, it’s automatically safe. I’ll also show you how to determine proper dosing and, of course, provide a list of relevant herb-drug interactions so you can make informed choices.
My goal with this article?
To give you the tools to use and prepare herbs with both informed caution and confidence. Many people refer to herbalism as the “original medicine”—and if that’s the case, we need to combine modern scientific knowledge with traditional practices. We need to treat herbs like medicine because, well… they are.
Herbal Pharmacognosy: Why It Matters
Understanding how herbs interact with the body is crucial—especially if you’re recommending them to others. But before we even talk about how the body processes herbs, we need to discuss pharmacognosy—the study of medicinal compounds found in nature.
Pharmacognosy is one of the oldest branches of pharmaceutical science, examining the morphological, chemical, and biological properties of natural substances. It covers not only plants but also mushrooms, marine life, microorganisms, and even minerals. (yes, nature is full of bioactive compounds!).
Some of the most well-known modern drugs—like morphine, aspirin (salicylic acid), digoxin, and taxol—all come from plants. In fact, about 25% of prescription drugs in the U.S. contain at least one active ingredient derived from plants (Arslan, 2014).
This is why pharmacognosy matters in herbalism—understanding the chemical constituents of an herb helps us determine how it works, how it’s best prepared, and whether it interacts with medications. It’s not just about tradition; it’s about science.
Herb-Drug Interactions: The Why & How
Herbs are not neutral substances—they have physiological effects, just like pharmaceuticals – that’s why we’re using them. And while concerns about herb-drug interactions are often exaggerated or based on hypothetical models, some interactions are very real.
A huge portion of the population is on at least one prescription drug. (Side note: This is also a reminder that consultations are non-negotiable if you’re recommending herbs to someone—you need to know every prescription, supplement, and occasional herbal blend they’re taking.) I know that it can seem daunting and intimidating to use herbs while on a prescription, or suggest to others that are, but here are a few important things to consider here:
Which Herb-Drug Interactions Actually Matter?
Not every herb-drug interaction you hear about is backed by solid research. Many are based on animal studies, test tube experiments, or theoretical assumptions rather than clinical human trials. Some are even performed with dosages so high; a human wouldn’t be able to replicate the same amount within a lifetime.
That said, some herb-drug interactions are serious, especially when dealing with medications that have a narrow therapeutic index (meaning small changes in dose can lead to toxicity or treatment failure).
The biggest concerns?
Cancer chemotherapy drugs
Blood thinners like warfarin
Heart medications like digoxin
If you’re on any of these, be extra cautious with herbs that can interfere with drug metabolism, absorption, or effectiveness. Not all interactions are hype—but not all are proven, either. The key is knowing which ones matter and making informed decisions (NCCIH).
My advice?
Understanding the herbs you work with is essential. You need to know how they are metabolized, their physiological effects, and their potential adverse reactions. Having a solid grasp of these three factors helps you determine whether an herb might interact with a prescription. But it doesn’t stop there—you’ll need to research the same three aspects of the medication and then compare them to assess any possible interactions.
St. John’s Wort (Hypericum perforatum) – The Herb-Drug Interaction King
It would be considered herbal blasphemy if I didn’t mention St. John’s Wort and drug interactions, so I’ll pay my due diligence.
While widely used for mild to moderate depression, its active constituent hyperforin is a strong inducer of metabolic enzymes—particularly CYP450 enzymes (CYP3A4, CYP2C9, CYP2C19) and P-glycoprotein (P-gp, ABCB1).
Translation?
It speeds up drug metabolism, often reducing the effectiveness of medications.
Serious Drug Interactions
Because of its effect on CYP3A4 and P-gp, St. John’s Wort has been linked to major drug interactions, including:
Organ transplant rejection – Lowered blood levels of cyclosporine, leading to acute heart and liver transplant rejection (Karliova et al., 2000; Ruschitzka et al., 2000).
Unintended pregnancies – Reduced effectiveness of oral contraceptives, resulting in breakthrough bleeding and accidental pregnancies (Bon et al., 1999; Hall et al., 2003).
HIV treatment failure – Decreased blood levels of indinavir and other antiretroviral drugs, risking treatment failure (Piscitelli et al., 2000).
Because of these risks, all St. John’s Wort products sold as herbal medicines must legally list contraindications, warnings, and precautions (EMA/HMPC, 2009).
How to Determine the Right Dose
So, how do you dose herbs safely?
Dosing depends on multiple factors:
The herb itself—some herbs are safe in high amounts, while others require precise dosing.
The formulation—tea, tincture, capsule, or decoction? Each has different extraction methods and potency.
The preparation—fresh vs. dried? Alcohol vs. water extraction? All of this changes potency and effects.
It can get confusing, so I highly recommend investing in a trusted reference book that you can refer back to. Here are my go-to resources for accurate herbal dosing:
Medical Herbalism – David Hoffmann (science-heavy, perfect if you love deep dives into phytochemistry!)
The Modern Herbal Dispensatory – Thomas Easley (great for DIY herbal formulations and dosing guidelines!)
Each herb has its own best method of preparation and dosage, so knowing how to use them correctly is essential.
Myth Buster: "If It’s Natural, It’s Safe"
Absolutely not. Get out of here with that.
Hippocrates—yes, the father of medicine—was allegedly poisoned by a plant (hemlock, to be exact). That should tell you something.
Paracelsus said it best: “The dose makes the poison.” This applies to everything—modern pharmaceuticals and herbal medicine. Some herbs can be toxic in the wrong dose or even at any dose. Let’s look at a few examples.
Pokeweed (Phytolacca americana) – This plant’s deep purple berries are tempting, but all parts of pokeweed are toxic. Ingestion can cause nausea, vomiting, diarrhea, and severe abdominal pain. The toxicity is due to alkaloids and saponins, which disrupt cell membranes, leading to irritation and poisoning (Evens et al., 2022).
Poison Hemlock (Conium maculatum) – Often mistaken for Queen Anne’s lace, this plant contains piperidine alkaloids, including coniine, which can cause muscle paralysis and respiratory failure. Even small amounts can be fatal (Bouzid et al., 2021).
Deadly Nightshade (Atropa belladonna) – Contains atropine and scopolamine, which interfere with the nervous system, leading to dry mouth, rapid heartbeat, hallucinations, and potential coma. Historically, it was used in cosmetics—yikes! (Pavlovic et al., 2024).
Final Thoughts: Knowledge is Power
Herbs are powerful medicine, but power doesn’t always mean safe. Whether an herb is beneficial or harmful depends on dose, preparation, and individual sensitivity. Proper identification, researching potential toxicities, and understanding safe dosages are non-negotiable.
When in doubt, consult a knowledgeable herbalist or healthcare provider.
I hope the goal of this article was achieved! Please feel free to contact with me with any questions 😊 As always, all likes, comments and shares are so greatly appreciated!
I’m always open to suggestions of topics you’d like to see covered.
Monday’s post will dive into the lymphatic system and herbs to help support its processes,
See you then,
Agy
PS. Thank you so much for your understanding and patience as this post was intended for Friday’s Beginner Herbal Series. I apologize for the delay!
Bibliography
Arslan, I. (2014). The importance of drugs of natural origin. Biomedicine International, 4(2), 109-121. PMC4204033.
Bouzid, D., et al. (2021). Case report on hemlock poisoning. Clinical Case Reports, 9, e04509. PMC8299090.
Evens, J., et al. (2022). Pokeweed exposures and their clinical outcomes. PubMed. PMID: 36332712.
Karliova, M., et al. (2000). St. John’s Wort and cyclosporine interactions. Guide to Pharmacology. Ligand 4726.
NCCIH. (n.d.). Herb-Drug Interactions. National Center for Complementary and Integrative Health. NCCIH.
Pavlovic, V., et al. (2024). Belladonna poisoning and antimuscarinic effects. PubMed Central. PMC11449552.
Piscitelli, S. C., et al. (2000). Herb-drug interactions with St. John’s Wort. Guide to Pharmacology. Ligand 6839.
Ruschitzka, F., et al. (2000). St. John’s Wort-induced transplant rejection. Guide to Pharmacology. Ligand 4726.
Soleymani, S., et al. (2017). Herb-drug interactions of St. John’s Wort: A systematic review. European Scientific Cooperative on Phytotherapy (ESCOP), 2018.
EMA/HMPC. (2009). Assessment report on Hyperici herba (St. John’s Wort). European Medicines Agency/HMPC.
Bon, S., Hartmann, M., & Kuhn, M. (1999). St. John’s Wort interactions with oral contraceptives. Guide to Pharmacology.
Veterinary herbalist here. Thanks for the succinct, accurate article on herbal safety. I see so many people just pouring herbs into their animals without working with someone who is knowledgeable! Sharing!
Super informative, I'm aware of the uses of St. John's Wort (although I haven't used it myself), but wasn't aware of the effects on other medication. And interestingly, referring to @Monica D.R.s comment about belladonna, this has been a staple in my home for years as an alternative to paracetamol, especially for headaches - but just adding my point, not answering!