They might not be able to pull you out of
a freezing lake, or carry you from a burning building, but plants have probably saved your
life, or at least made you feel a whole lot better. That’s because, at least in the U.S., a
quarter of all prescription drugs come from substances that are found only in plants. We humans have a long history of using plants
to treat diseases. Most of those treatments were probably discovered
using blind luck — like, by people munching on random leaves and seeing how they felt. If they found one that seemed to work, the
knowledge would usually get passed around by word of mouth, but sometimes it would also
be written down. That’s how we ended up with recipes that
are about as old as writing itself — like the 5000 year old Sumerian clay slab that
lists 250 plants for preparing medicines. Of course, the recipes don’t always work,
and there are plenty of old herbal remedies that do absolutely nothing. But a few did
work — and we still use some of them in medicines today. Many of the plant-based substances people
use belong to a broad group of bitter-tasting, nitrogen-containing compounds called alkaloids. These compounds don’t seem to be strictly
necessary for plants to survive, so they probably offer evolutionary bonuses – like a defense
against anything that tries taking a bite out of it. Their names mostly end in i-n-e, and you’ve
probably already heard of some of them, like caffeine, nicotine, morphine… And a lot of them have effects on our bodies
that are pretty strong … for better or worse. Take the deadly nightshade, for example. In 2009, a woman was hospitalized from eating
just six nightshade berries, which she thought were blueberries. Ten berries could have been
fatal. One of the killer compounds in nightshade
is atropine, an alkaloid found all over the plant. But atropine also has a good side — it’s
actually on the World Health Organization’s “Model List of Essential Medicines” in
three separate places! Surgeons can use it as a sedative for short
operations, or to dilate the pupils to gain easy access to the back of the eye. And, despite being extracted from a plant
so toxic, atropine works an antidote against certain types of poisoning! Some pesticides and nerve gases overwork the
parasympathetic nervous system, and atropine can counter that deadly effect by blocking
the receptors these toxins over-activate. Other useful plant-based drugs took a lot
of hard science to make work — as in the case of an anti-malarial drug called artemisinin. The compound comes from the sweet wormwood
plant, and Youyou Tu, the chemical engineer who developed it, was awarded half of the
Nobel Prize for Medicine in 2015. Using plants to treat malaria is not a new
thing. The disease has probably killed half of all humans from the Stone Age to today,
and we haven’t beaten it yet. With so many people suffering, especially
in developing countries, it’s not surprising people turned to plants for a cure. Around the world, more than 1200 plant species
are used to treat malaria and the fever that comes with it. But only a fraction of these
have been properly tested for their effectiveness. One of the first remedies known to be genuinely
effective was quinine, an alkaloid that comes from the bark of Peruvian cinchona trees. A compound known as chloroquine, which was
based on quinine, was later developed synthetically as a safer and more potent version of the
drug. But it wasn’t long before the Plasmodium
parasite that causes malaria started showing resistance to chloroquine. So people started
looking for an alternative. Tu and her team turned to traditional remedies
from China. They scoured thousands of traditional recipes for potions and medicines that were
said to reduce fever, looking for the most promising plants. They found a clear winner. One plant — the
sweet wormwood — showed up in not just one or two, but hundreds of different recipes. Initial tests of sweet wormwood extracts on
the malaria parasite were promising, but inconsistent. Some experiments showed sweet wormwood to
be highly effective, but others only slightly. Tu thought that the variations might be caused
by differences in the way the wormwood extract was prepared, so she went back to the old
texts to find more clues. Most of the remedies suggested processing
dried leaves with boiling water, but Chinese philosopher Ge Hong, writing in the year 340
CE, had a different suggestion. He described a preparation process that used
fresh, not dried leaves, and involved extracting the juice by soaking those fresh leaves in
cold water, wringing them out, then drinking the juice straight down. Based on this account, the team developed
their own extraction method using ether, then tested it out on mice, monkeys, and finally
people. And it worked! The new-and-improved extract killed off malaria
parasites soon after they entered their host’s red blood cells, and with relatively mild
side effects. The active compound was called artemisinin after the plant it was found in. The discovery of artemisinin created a whole
new family of antimalarial drugs that are still used to treat malaria today. Then there’s diabetes, another disease that
people have been trying to treat for a long time. Uncontrolled blood sugar levels in people
with diabetes can lead to complications like nerve damage, sight problems and kidney failure. But plants have our backs on this one, too. For the estimated 400 million people who have
Type II diabetes, one of the most widely prescribed treatments is metformin, a relatively simple
molecule that’s made up of just a few nitrogen, carbon, and hydrogen atoms. The story of metformin starts with an herb
known as goat’s rue, or professor weed. It stands over a meter high, with white, blue,
or purple flowers. Professor weed has been used to manage diabetes
around the Middle East and Europe since the Middle Ages. In the late 1800s, studies found that the
plant contained high levels of an alkaloid called guanidine. When isolated, guanidine
worked great at reducing blood sugar levels in animals, but it was too toxic to use in
people. So chemists got to work, trying different
adaptations of guanidine that kept the blood sugar down, but without the whole poisoning
problem. The result was metformin. Safe, effective
and cheap to make, metformin is helping millions of people manage their diabetes. Despite its simple chemical structure and
plenty of research, we still don’t really know how metformin lowers blood sugar, or
why it’s so effective with so few side-effects. So, what thanks do the American people give
this life-saving plant? We slap it on the Noxious Federal Weed list! But, to be fair, that’s because it’s an
invasive species in the US. It’s a lot less destructive when it grows in the Middle East,
Europe and Asia. Not all plants are so common, though — in
fact, plants containing the secrets to much-needed cures may have gone extinct before we had
the chance to even name them, let alone study them. And we’ve come close to losing life-saving
plants before. In 1987, for example, a botanist named John
Burley trekked through a swamp forest in Malaysia, collecting plant samples to study back in
the lab. His travels were part of a larger mission to find new treatments for various
cancers, as well as HIV. One of these samples, tagged “Burley-and-Lee
351” didn’t kill cancer cells, but it did do an amazing job of preventing HIV from
replicating. So the collectors high-tailed it back to the
forest… only to find it gone, cut down for firewood or building. Extracts from similar
trees didn’t have the same effect, because they were slightly different species. It was only salvaged when a few trees of the
right species were found at the Singapore Botanical Gardens. The drug is called Calanolide
A, and it’s currently in Phase II clinical trials and owned by the local Malaysian government. Then there’s this pretty little thing — the
Rosy Periwinkle. It might look like something that would be
right at home in my backyard, but it’s actually native only to Madagascar – though it will
happily grow anywhere warm. The native people of Madagascar used these periwinkle plants
for all kinds of ailments. In the 1950s, researchers from Western pharmaceutical
companies studied the periwinkle and discovered that it contained some rather remarkable alkaloids. Two of these, called vincristine and vinblastine,
are used to treat certain types of cancer by stopping the cells from dividing. Vincristine has helped increase success rates
in treating kids with leukemia from just 10% in the 1960s, to well over 80% today. And vinblastine is often a core chemotherapy
component for lymphoma — a cancer of the lymphatic system — as well as testicular
cancer. All kinds of plants have amazing substances
locked away inside them. So the next time you walk past a tree or flower, give it a
pat on the leaf — assuming it’s not, like, thorny, or poisonous to the touch- anything
like that. You might look a little strange, and the plant
won’t understand, but it probably deserves it anyway. Thanks for watching this episode of SciShow,
which was brought to you by our patrons on Patreon. If you want to help support this
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