Plants gave us Taxol and digoxin, yet the herb isn’t the drug

Key takeaways

• The cancer drug Taxol started with Pacific yew bark collected for the National Cancer Institute in 1962, and it took until 1992 to win FDA approval.
• From 1981 to 2019, about a third of new small-molecule cancer drugs were natural products or made directly from them, and nearly two-thirds counting drugs built on natural blueprints.
• When a poison center bought 10 weight-loss products sold online as tejocote and had them tested, 9 were yellow oleander, a plant with a heart toxin that acts like digoxin.
• FDA’s botanical drug pathway lets a plant mixture be approved as a medicine, but FDA lists only four products that have made it.
• Never swap a prescribed plant-derived medicine for the herb it came from, and call Poison Control at 1-800-222-1222 if a botanical product makes you sick.

In 1962, a U.S. Department of Agriculture botanist named Arthur Barclay collected bark from Pacific yew trees in the Pacific Northwest for the National Cancer Institute (NCI)¹². It was one of about 30,000 natural samples that NCI and USDA researchers screened for cancer-fighting activity from 1960 to 1981¹.

In 1964, chemists Monroe Wall and Mansukh Wani found that the yew extract was toxic to living cells. They isolated its most active compound and named it paclitaxel¹.

Then came three decades of animal studies, human trials, a supply crisis and a new way to make the drug. The FDA approved paclitaxel, sold as Taxol, for ovarian cancer in 1992¹. Susan Band Horwitz, whose lab worked out how it kills cancer cells, later called it the first billion-dollar drug².

The yew’s story holds the whole lesson of plant medicine. The plant supplied the molecule. Chemistry, testing and careful manufacturing turned it into something a doctor can dose.

That gap between the herb and the drug is what this article is about. It explains where famous medicines came from, why the plant itself is not the medicine, and how the FDA handles medicines that stay plant mixtures.

Bark, leaves and flowers gave medicine some of its biggest drugs

Here is a short field guide to plants that changed medicine.

Plant	Medicine it led to	A key moment
Foxglove	Digitalis drugs, including digoxin	William Withering documented foxglove treatment in 17853
Opium poppy	Morphine	Friedrich Sertürner isolated it from opium in the early 1800s4
Cinchona tree bark	Quinine	French pharmacists Pierre Joseph Pelletier and Joseph Caventou isolated it in 18204
White willow bark	Aspirin	Salicin from the bark was the starting point for aspirin5
Rosy periwinkle	Vincristine	An alkaloid now used against leukemia3
Pacific yew	Paclitaxel (Taxol)	FDA approval for ovarian cancer in 19921
Snowdrop	Galantamine	A compound now used for Alzheimer’s disease5
Goat’s rue	Metformin	Guanidine, a compound found in the plant, was shown to lower blood sugar in 19186
Sweet wormwood	Artemisinin	A malaria drug WHO credits to traditional medicine7

Foxglove was already a known herbal remedy when Withering documented it in 1785³. What changed was careful study of its dose range and its toxic effects³. That step, from folk remedy to measured treatment, is the hinge of this whole story. Foxglove’s digitalis drugs are still often used to control heart rate³.

Quinine shows how fast purification can spread a medicine. Pelletier and Caventou never patented their method, and by 1826 they were making more than 3,500 kilograms of quinine sulfate a year⁴. The pure drug went on to replace the bark as the standard malaria treatment⁴.

Some of these stories also involve the knowledge of healers and communities. Our article on traditional knowledge tells how goat’s rue led to metformin and how an ancient Chinese recipe led to artemisinin, and asks who should benefit.

Nature still shapes new drugs, especially for cancer

The World Health Organization (WHO) says more than 40% of pharmaceutical formulations are based on natural products⁷.

Since 1997, a series of reviews by researchers David Newman and Gordon Cragg has tracked where new drugs come from⁸. Their 2020 update in the Journal of Natural Products covered drugs approved from 1981 to 2019⁸. Cragg, a former chief of NCI’s Natural Products Branch, was the scientist tasked with finding enough Pacific yew to produce Taxol⁹.

Cancer is where nature’s role is clearest. Of 185 small-molecule cancer drugs approved from 1981 to 2019, 62, or 33.5%, were natural products or made directly from them⁸. Add 58 synthetic drugs built around a natural product’s core structure or designed to mimic one, and the share reaches 64.9%⁸.

The earlier era leaned even harder on nature. From 1946 to 1980, 40 of 75 small-molecule cancer drugs, or 53.3%, were natural products or their derivatives⁸.

Newman and Cragg also checked a popular alternative. Combinatorial chemistry builds huge libraries of synthetic molecules by the thousands. By their count, it had produced only two entirely new approved drugs in 39 years, and they called one of those a little speculative⁸.

One caution about these numbers: “natural product” is broader than “plant.” The authors note that many natural-product drugs and leads come from microbes⁸. Plants are a big part of the story, not all of it.

Why the plant isn’t the drug

If a plant gave us a medicine, why not take the plant? Three reasons.

The dose moves around. The FDA describes plant products as complex mixtures whose chemical makeup is often poorly defined, and it expects variation from batch to batch¹⁰. A pill made from a purified compound holds a measured amount. A handful of leaves does not.

Look-alike plants can kill. In September 2022, a 23-month-old got sick after eating a weight-loss product labeled as Mexican tejocote root that the child’s mother had bought¹¹. The child had vomiting, a slow heartbeat, low blood pressure and abnormal heart tracings, and needed two doses of an antidote used for digoxin overdose¹¹.

Suspecting a mislabeled product, New Jersey’s poison center bought 10 products sold online as tejocote, a plant promoted for weight loss¹¹. Nine contained yellow oleander, and none showed any tejocote root¹¹. Yellow oleander carries thevetin B, a heart compound with effects like digoxin’s and the potential to poison¹¹.

The FDA issued its own warnings in 2023. Seeds and capsules sold for weight loss as “Nuez de la India” turned out to be yellow oleander¹². The harmless candlenut seeds they were supposed to be look much like the toxic ones¹².

Here is the hard truth inside that case. The same kind of chemistry that makes foxglove useful, compounds that strongly change how the heart beats, makes other plants with similar compounds dangerous when nobody knows what’s in the bag.

Even a pure compound needs a delivery system. Taxol barely dissolves in water. It had to be mixed with a solvent called Cremophor, which caused allergic-type reactions, so patients received steroids and antihistamines first².

Mistaken plants can do slow damage, too. Our traditional knowledge article describes how a mix-up between two herbs caused kidney failure and cancer in Belgium.

From bark to vial: six steps the yew had to pass

Use this table as a tool. The middle column shows what turned yew bark into Taxol. The right column turns each step into a question you can ask about any herbal product.

Step	What happened with Taxol	Ask this about an herbal product
1. Get the right plant and part	A USDA botanist collected Pacific yew, and early lab tests pointed to the bark12	Is the species and plant part named, and was its identity tested?
2. Find the active compound	Wall and Wani isolated paclitaxel in 19641	Does the label say which compound matters and how much is in a dose?
3. Learn how it works	In 1979, Horwitz showed it blocks cell division in a new way1	Is there a tested explanation, or only a story?
4. Test it in people, step by step	NCI chose it for clinical development in 1977, and a 1989 trial found 30% of advanced ovarian cancer patients responded1	Have controlled human trials tested this product for your condition?
5. Make it reliably	Bark to vial took about 18 months and supplies ran short, so NCI and Bristol-Myers Squibb moved to a semisynthetic process in 199112	Does the maker test every batch?
6. Keep learning after approval	Breast cancer approval followed in 1994, and a newer form was approved for pancreatic cancer in 20131	Are side effects tracked and reported?

Notice how long the middle steps took. Ten years passed between Horwitz’s 1979 finding and the 1989 ovarian cancer trial¹.

FDA has a path for plant mixtures, and only four products have finished it

Not every plant medicine has to become a single molecule. The FDA defines a botanical drug as a product made from plant materials, algae or large fungi and intended to diagnose, treat or prevent disease¹³. It can come as a tea, powder, tablet, capsule, tincture, skin product or injection¹³.

The rules bend for mixtures. Developers don’t always have to pin down which ingredients are active¹⁰. Instead, FDA judges consistency through the “totality of the evidence”: control of the raw plant material, chemical testing and manufacturing controls, and biological tests plus clinical data¹⁰¹³.

Past use counts for something. If a plant was lawfully sold as a dietary supplement and the proposed use is similar, early human studies may begin without new animal testing¹⁰. FDA finalized its first botanical guidance in June 2004 and updated it in December 2016¹³¹⁰.

Yet the finish line is rarely crossed. FDA lists three botanical new drug applications and one biologic application as approved¹³:

Product	Plant source	Approved use	Year
Veregen (sinecatechins)	Green tea	Genital warts	2006
Mytesi (crofelemer)	Latex of the Croton lechleri tree	Non-infectious diarrhea in adults with HIV on antiretroviral therapy	2012
NexoBrid (anacaulase)	Enzymes extracted from the pineapple plant	Thermal burns	2022 for adults, 2024 for children
Filsuvez (birch triterpenes)	Silver birch	Wounds from dystrophic and junctional epidermolysis bullosa, a fragile-skin disease	2023

Dates and uses come from a review of approved U.S. botanical drugs¹⁴. Two common plants, psyllium and witch hazel, can also be sold over the counter under FDA’s drug monographs, standard rules for nonprescription drugs¹³.

The gap with supplements is wide. Under FDA rules, products meant to diagnose, treat or prevent disease are generally regulated as drugs¹⁰. A supplement made from the same plant has not passed that review, which is why its label can’t promise a cure. Our article on supplement label claims explains those rules.

Where the next plant medicines may come from

NCI still keeps a library of nature. Its Natural Products Repository holds more than 200,000 extracts of plants, marine life and microbes, gathered through collection programs in 25 countries⁹. Researchers across the United States still request samples from it⁹.

WHO sees several routes forward. At its 2023 traditional medicine summit, it said ethnopharmacology and reverse pharmacology could help identify new drugs, and genomics and artificial intelligence could expand knowledge of traditional medicine¹⁵.

Ethnopharmacology studies how communities use plants as medicine. Reverse pharmacology starts from remedies people already use and works backward to test what they do and how.

WHO paired that optimism with a caution. Natural products are not automatically safe, and long use does not prove a remedy works¹⁵.

Supply matters, too. Early Taxol came from bark, and the shortage eased as researchers found a renewable source that didn’t require destroying yew trees². A medicine that depends on stripping wild plants can strain the very species it comes from.

What the evidence says about plant medicines

Here is how different kinds of plant products rate on our four-level evidence scale.

Product type	Evidence level	What the record shows
Purified plant-derived drugs, such as paclitaxel, used as prescribed	Strong evidence	Staged human trials before approval, such as a 30% response rate in advanced ovarian cancer1
FDA-approved botanical drugs, for their approved uses	Strong evidence	Passed FDA drug review, including batch-consistency standards1013
New leads from natural-product extract libraries	Promising but early	Large libraries feed discovery, but screening is only the first of many steps19
Raw herbs used in place of a drug made from them	Not enough evidence	Plant mixtures vary from batch to batch and rarely go through drug review1013
Online “tejocote” or “Nuez de la India” weight-loss products	Evidence says no, or unsafe	Tested products often turned out to be toxic yellow oleander1112

Respecting plants means respecting their strength

If you believe plants hold real healing power, history agrees with you. Foxglove, the opium poppy, cinchona bark and the Pacific yew each changed medicine.

That power is exactly why dose matters. The turning point for foxglove was learning where its benefit ended and its toxicity began³. Yellow oleander shows what happens when nobody measures at all¹¹.

Respect also means credit. WHO credits traditional medicine as the origin of drugs such as aspirin and artemisinin⁷. That knowledge was held by healers and communities long before chemists arrived. Honoring that knowledge and testing it carefully are two halves of the same job.

A few habits keep you safe:

• Never swap a prescribed plant-derived medicine, such as digoxin or a cancer drug, for the plant it came from.
• Tell your clinician and pharmacist about every herb and supplement you take.
• Skip weight-loss roots and seeds sold online as tejocote or Nuez de la India¹¹¹².
• Store supplements where children can’t reach them.
• If nausea, vomiting, dizziness or an irregular heartbeat follows a botanical product, call Poison Control at 1-800-222-1222, or 911 for serious symptoms¹².
• Report problems to the FDA at 1-888-INFO-FDA (1-888-463-6332)¹².

Questions readers ask

The bottom line

Plants have given medicine some of its most important drugs, from foxglove’s digoxin to the yew’s paclitaxel, and natural products still shape a large share of new cancer drugs. That history is a strong argument for studying plants seriously and protecting the species and knowledge behind them.

It is also a warning. The herb is not the drug. Purification, dosing, testing and consistent manufacturing are what turn a powerful plant into a reliable medicine, and look-alike plants sold online show what happens when those steps are skipped. Respect the plant, and respect the dose.

Related reading

• An ancient recipe led to a Nobel prize, and new treaties ask who benefits
• Traditional medicine got WHO codes, and testing it fairly is the harder part
• How to judge a cup of herbal tea, which is gentle but not automatically harmless
• What gets into supplements that isn’t on the label
• Why supplement labels say ‘supports’ and never say ‘cures’

Sources

1. National Cancer Institute. “Natural Compound Helps Treat Breast and Ovarian Cancers” (Taxol discovery timeline). NCI, accessed October 2026. cancer.gov
2. National Cancer Institute, Developmental Therapeutics Program. “Taxol” video transcript (Susan Band Horwitz and colleagues). DTP Timeline, accessed October 2026. dtp.cancer.gov
3. Sinskey AJ. “History & Overview of the Pharmaceutical/Biotechnology Industry.” Lecture notes, Principles and Practice of Drug Development (15.136J), MIT OpenCourseWare, 2013. mitocw.ups.edu.ec
4. Jovanović A, Krajnović D. “The Developmental Path of Quinine: What Can We Learn from History?” Acta Medica Medianae, 2023. publisher.medfak.ni.ac.rs
5. Dias DA, Urban S, Roessner U. “A Historical Overview of Natural Products in Drug Discovery.” Metabolites, 2012. pubmed.ncbi.nlm.nih.gov
6. Bailey CJ. “Metformin: historical overview.” Diabetologia, 2017. research.aston.ac.uk
7. World Health Organization, Global Traditional Medicine Centre. “About.” WHO, accessed October 2026. who.int
8. Newman DJ, Cragg GM. “Natural Products as Sources of New Drugs over the Nearly Four Decades from 01/1981 to 09/2019.” Journal of Natural Products 83(3):770–803, 2020. pubmed.ncbi.nlm.nih.gov
9. National Cancer Institute, Division of Cancer Treatment and Diagnosis. “In Memoriam: Dr. Gordon Cragg.” NCI, 2025. dctd.cancer.gov
10. U.S. Food and Drug Administration. “Botanical Drug Development: Guidance for Industry.” FDA, December 2016. fda.gov
11. Berland N, Kababick J, Santos C, Calello DP. “Notes from the Field: Online Weight Loss Supplements Labeled as Tejocote (Crataegus mexicana) Root, Substituted with Yellow Oleander (Cascabela thevetia), United States, 2022.” MMWR, CDC, September 15, 2023. cdc.gov
12. U.S. Food and Drug Administration. “FDA Expands Warning to Consumers About Toxic Yellow Oleander Purported to be Nuez de la India in Certain Botanical Weight Loss Products.” FDA safety alert, content current as of September 8, 2023. fda.gov
13. U.S. Food and Drug Administration, Center for Drug Evaluation and Research. “What Is a Botanical Drug?” FDA, content current as of September 3, 2026. fda.gov
14. Journal of Integrative Dermatology. Article on FDA-approved botanical drugs (corresponding author Peter Lio, Northwestern University Feinberg School of Medicine), Table 1: “Currently approved botanical drugs in the United States.” Article title and date not displayed on the page; accessed October 2026.
15. World Health Organization. “WHO convenes first high-level global summit on traditional medicine to explore evidence base, opportunities to accelerate health for all.” News release, August 10, 2023. who.int