Nature's pharmacy: the discovery of medicinal plants

Giovanbattista della Porta was an educated Italian nobleman from the mid-16th century, and an important figure in the beginnings of the Renaissance.

He founded the first scientific society, the Academia Secretorum Naturae, and made important advances in philosophy, literature and science.

Della Porta was a leading thinker of his day, and like Galileo, his scientific curiosity caught the attention of the Church and the Inquisition, a problem that plagued him throughout his career.

Phytognomica, one of his botanical works, is a paradoxical mix of his modern thinking, and continued adherence to medieval folklore, such as the “doctrine of signatures.”

The doctrine states that a plant's physical appearance is a "signature" of its use in treating human ailments.

Toothwort, for example, was believed to be effective in treating toothache.

Here, della Porta highlights the physical similarities between the pomegranate, human teeth, and pine cones.

Under the doctrine of signatures, these plants were thought valuable in treating tooth-related problems.

Elizabeth Blackwell, working 200 years after della Porta, gave a different description of toothwort’s medicinal properties.

In her major work A Curious Herbal, the first herbal written and illustrated entirely by a woman – she catalogued British plants and their medicinal uses.

Blackwell emphasized the “calming properties” of toothwort, and its value for sleeplessness and epilepsy, rather than any relation to teeth.

By this time, studies of the medicinal uses of plants had advanced substantially beyond the “doctrine of signatures.”

While medicinal uses of toothwort are embedded in northern European tradition, uses of opium began in western Asia, the Middle East and the eastern Mediterranean.

The beneficial effects of drugs like morphine have been enormous, but so have the negative and narcotic impacts – from the opium wars of the early 19th century to the contemporary opioid crisis.

This is the cover of Opiologia, a vast 1682 treatise on the opium poppy, by German physician Georg Wolfgang Wedel.

Wedel sought to understand how chemical compounds impacted human behavior.

His massive research output reflected the huge growth of opium-based treatments in Europe.

Wedel noted opium's potential benefits, but also its lethal characteristics:

“Opium is a life-anchor for him who uses it properly and with circumspection, but in the hands of the unskilled it is a semblance of Charon’s boat, and pernicious as a sword in the hands of a madman.”

For centuries, opium had been used widely in Europe for treating all kinds of illnesses.

But in the early 19th century British smuggling of opium into China from India had disastrous social consequences.

And when the China tried to crack down on the opium trade, Europe retaliated.

The Opium Wars opened up China to European imperial and trade interests – a turning point that many historians view as the beginning of modern China.

The opium, at the center of this international conflict, would be harvested from the seed heads of the poppy, as shown here.

Another plant with potent chemical and narcotic properties, and a history as long and complex as that of opium: cannabis.

Originating in central Asia, cannabis was bred by people into two forms, one for the production of useful fibers, and the other for its narcotic properties.

By the 1500s, its production and use in Europe was well established.

These illustrations from Rembert Dodoens’s Stirpium Historiæ Pemptades Sex accompany descriptions of the then-current medicinal uses for the cannabis plant, including as a treatment for sleeplessness.

Published in Latin, Dodoens’ work became a key reference in Europe for information about the uses of plants of all kinds.

60 years later, English botanist John Gerard translated it to English, embellishing it with information from other botanists such as Mattioli, Bock, L’Obel and Fuchs.

Gerard’s publication of the work as his own was controversial, but its impact was profound.

In the work, he describes uses for “hempe”, including one seemingly no longer in use: “the feed given to the hens causeth them to lay eggs more plentifully.”

The use of hemp seed was often emphasized in early medicinal texts, including in A Curious Herbal, from the mid-eighteenth century.

Here, Elizabeth Blackwell refers specifically to the importance of growing the female hemp plant.

Cannabis is a species that has separate male and female individuals, and for the medicinal purposes Blackwell describes, seeds are essential - requiring female rather than male hemp plants.

Boiled in milk, Blackwell recommends hemp seed as a treatment for coughs and jaundice.

People have moved useful plants around the world since the early days of human history.

In the early modern era, the exchange of plants across continents accelerated with maritime trade and European colonial expansion.

On this page, Rembert Dodoens compares “Aloe” with “Aloe ex America.”

On the right, “Aloe ex America”, is probably in fact agave (similar to true Aloe vera) from the deserts of the New World.

The true Aloe is from the Old World, and has been used for centuries for its soothing properties. Dodoens describes the plant's origins and medicinal properties.

We end with the foxglove, a plant forever linked to late 18th century English physician William Withering.

Its use in medicinal treatments began well before Withering. Elizabeth Blackwell had recorded the plant as an emetic over four decades earlier, and it had been used in folk treatments for centuries before that.

But Withering’s work, An Account of the Foxglove, and Some of Its Medical Uses, was the first comprehensive examination of the plant as it related to medicine.

Withering examined foxglove leaf extracts for treating dropsy, another term for edema, the bodily swelling that often precedes heart failure.

Its emetic properties, when used in the right amounts, could be life-saving.

But his analysis noted that high doses of foxglove extract could also be fatal.

The carefully reasoned and systematic examination of a plant’s medical uses seen in Withering’s work marks the beginning of the transition from an archaic understanding of plants to the many discoveries of plant-based drugs that have characterized modern science, which we examine in more detail in – The People and Plants Shaping Modern Medicine.