Medicinal and useful plants

Colour botanical plate: a poppy stem with white and red flowers, surrounded by numbered drawings of flowers, stamens, a capsule and seeds. — The opium poppy: the flowering plant, its parts, its ripe capsule and its seeds, a botanical plate from the collection Köhler’s Medizinal-Pflanzen (1897). Franz Eugen Köhler (Köhler's Medizinal-Pflanzen, 1897), Public domain, source

A plant does not make medicines: it makes defence molecules.

⚠ This page is not for treating yourself.

It provides no uses, no preparations and no dosages, and it does not enable anyone to identify plants. Any health question is a matter for a qualified health professional.

Why plants heal

A plant does not make medicines. It makes defence molecules — substances meant to keep insects away, to slow down fungi, to deter herbivores. It has no interest in healing us, and the fact that one of these molecules acts on the human body is a happy accident.

This accident can be explained. Living things have shared a common chemistry for hundreds of millions of years: a molecule designed to disrupt a caterpillar’s nervous system can disrupt ours, sometimes usefully. Any substance becomes a poison if the dose is too high; some, at low doses, can heal. This is a central idea in pharmacology, but it never says which dose is safe.

In a plant, this active substance amounts to almost nothing — often a very small fraction of the mass — and its quantity varies with the individual plant, the season, the soil and the part used. This is what makes the whole plant a hazardous remedy: one does not know exactly what dose one is taking. The pharmacist’s work has consisted of identifying the molecule responsible, then isolating it so that it can be dosed.

Two examples tell the story of this journey.

Willow bark had been used since antiquity against pain and fever. In the nineteenth century, salicin was extracted from it; chemists derived salicylic acid from it, then a modified form, developed in an attempt to irritate the stomach less: aspirin. The poppy, for its part, produces a latex, opium, from which morphine was isolated around 1804 — it is often seen as the first pure active substance extracted from a plant.¹

The move from plant to molecule is not a technical detail. It is what turns a use into a medicine, because it makes possible what no traditional preparation allows: giving exactly the same quantity every time.

“Natural” does not mean “safe”

Many plants are toxic, some fatally so. Others interact with medical treatments and can make them ineffective or dangerous.

A plant cannot run away: it defends itself through chemistry. The molecules it synthesises exist for its own survival against predators, not to be useful to us.

What heals and what poisons is often simply a question of dose.

What medicine owes to ancient knowledge

The aim is not to repeat that other cultures “knew things”, but to identify what modern medicine still makes use of.

Artemisinin: from a Chinese text to the Nobel Prize

The clearest example of this approach is the discovery of artemisinin, a major treatment for malaria.

The researcher: Tu Youyou, at the Academy of Traditional Chinese Medicine, in Beijing.
The project: Project 523, a Chinese research programme launched in 1967.
The recognition: Nobel Prize in Physiology or Medicine, in 2015.²

The story is valuable above all for the way it began — and it did not begin with an inspired reading.

An extract of sweet wormwood (Artemisia annua) had shown promising inhibition of the parasite. Then the result could not be reproduced. It even contradicted what the literature said.³

That is the real starting point: a result that refuses to come back.

To understand why, the team undertook an exhaustive review of the ancient literature. It found a single mention of this plant against the symptoms of malaria, in Ge Hong, in the fourth century:⁴

“A handful of qinghao immersed with 2 liters of water, wring out the juice and drink it all.”⁵

An ordinary sentence. But Tu Youyou noticed what was missing in it: there is no boiling.

Hence the hypothesis: the heat used in their own extraction method was perhaps destroying the active substance.⁶

They started again at low temperature. The activity became much better.⁷

They finally obtained an extract 100% effective against the parasite, in mice as in monkeys.⁸

The sequence of events deserves a pause. The ancient text did not provide the remedy: it provided a clue about method. And that clue was only useful because a team kept stumbling over a result it could not reproduce, and refused to ignore it.

This case brings together a researcher, an ancient clue and a measurable molecule: Ge Hong’s recipe, for its part, is not a treatment.

Cinchona: dismantling a received idea

The word “quinine” comes from the Quechua kina, meaning bark. The name of the medicine preserves a trace of the language of those who knew the tree (Cinchona).

A widespread account

The Andean peoples had always treated malaria with this bark, and the Europeans supposedly stole this knowledge from them.

What historians debate

Absence of the disease: The Indigenous populations of the Americas do not carry the genetic adaptations to malaria at significant frequencies: the disease has either always been absent there or has been present for less than several centuries.
A different initial use: The earliest Spanish accounts document a use of the bark against fevers and various ailments; its precise link with malaria is still debated by historians.
Post-contact hypothesis: For these historians, the antimalarial use is thought to have arisen from the encounter between the imported disease and the local pharmacopoeia.⁹

The indispensable Andean contribution

There are more than twenty species in the genus Cinchona, whose concentrations of active principles (quinine and cinchonine) vary from one species to another, and even from one population to another.¹⁰

Without the expertise of Andean botanists and healers, the Europeans were unable to distinguish the effective species from the inactive varieties. In this reading, the contribution of Andean knowledge lies above all in the classification and identification of the effective species.¹¹

The decision of 1820

In 1820, the French pharmacists Pierre-Joseph Pelletier and Joseph Bienaimé Caventou isolated pure quinine from the bark.¹²

They chose not to patent their manufacturing process, publishing their work so that global public health could benefit from it.

Access to biological resources and traditional knowledge raises the question of how the economic benefits are shared between industrialised countries and Indigenous populations.

This area is now regulated, for the states that have ratified it, by the Nagoya Protocol (2010) on access to genetic resources and the fair and equitable sharing of benefits arising from their utilisation.¹³

Plant origin of medicines: getting the facts right

A frequent claim holds that a fixed proportion (e.g. 50% or 80%) of all medicines are directly derived from plants.

The reference survey is that of David Newman and Gordon Cragg, who reviewed nearly forty years of approved medicines. For small-molecule anticancer drugs approved from 1981 to 2019, they count 33.5% natural substances (not only plant-derived ones) or direct derivatives, and 64.9% if synthetic molecules built on a natural model are added. Classic, older examples: aspirin, morphine; a more recent one: paclitaxel, an anticancer drug.¹⁴

The gap is a matter of definition, not of uncertainty: depending on whether one counts only molecules of natural origin and their direct derivatives, or also molecules merely inspired by a natural model, the proportion goes from about a third to nearly two thirds. One must always know what a figure counts before comparing it with another.¹⁵

Note 1

Säure im Opium ; An Account of the Success of the Bark of the Willow in the Cure of Agues

Acid in Opium ; An Account of the Success of the Bark of the Willow in the Cure of Agues

Sertürner, Friedrich, “Säure im Opium”, Journal der Pharmacie, 1805-1806

first refined willow bark into yellow crystals and named it Salicin […] produced a stronger compound from the crystals isolated from willow bark, which he named salicylic acid […] decided to develop a form of salicylate that did not cause gastric irritation

Desborough, M. J. R. and Keeling, D. M., “The Aspirin Story – from Willow to Wonder Drug”, British Journal of Haematology, vol. 177, 2017, p. 674-683