Many of our current drugs were originally derived from plants and fungi. Use of plants for medicinal purposes undoubtedly involved trial and error and since communication between societies was unlimited until relatively recently, very little knowledge was brought in from outside. Egyptians left records of 700 formulas for medicinal purposes (3500 ybp).

Hippocrates - father of medicine, rational approach to treatment, 300-400 medicinal plants

Aristotle - compiled list of medicinal plants

Theophrastus - Aristotle's star pupil, father of Botany

Dioscorides - largest and most complete work until 14th century - De Materia Medica. Standard reference work for doctors and pharmacists. Codex Juliana is an elaborate copy of De Materia Medica that was made for a Roman emperor's daughter around 500 A.D. This book is now in Vienna. Modern reproductions of this book were available recently.

Very little else done in the West until theRenaissance, people in Dark Ages and Middle Ages felt that they could not do anything that was as good as the work of the Greeks so they were reluctant to try to improve on Classical works.

Renaissance

Paracelsus - Presented idea that God had provided signs in plants as to their proper use - Walnuts for brain disorders, Hepatica (liver leaf) for liver ailments, etc. Idea was obviously wrong but he at least tried something new. Something happened to Western attitudes during the Renaissance, they had enough confidence to do original work and challenge the work of the Ancients.
The 17th and 18th Century saw the development of hypothesis testing in medicine which replaced the wild speculation and rumors that were common. Anesthesia was introduced in the 19th century by a dentist in a small town in Georgia who used volatile chemicals (I believe chloroform) to throw parties with his friends. He realized that these chemicals could be used to control pain. The 20th century has seen an explosion of development of new procedures and drugs, many to deal with health problems caused by bad habits and improper diets.

Many modern medicines are derived from fungi (antibiotics, especially) and these will not be discussed here.

Green Plant Products

Oils and gums - purgatives, carriers, emulsifiers

Volatile oils and resins - antiseptics

Steroids and Alkaloids - often occur as glycosides (sugar molecule(s) attached). The glycoside is often the active form

Steroid backbone Testosterone

Steroids occur in many unrelated plants, probably as feeding deterrents. An interesting example of the ability of insects to take advantage of plant products is the relationship between Monarch butterflies and milkweeds. The monarch lays its eggs on milkweeds and the larvae accumulate the steroids contained in these plants. These compounds make the butterflies poisonous to predators throughout their lives.

Animal hormones are steroids. Since the steroid "backbone" is complex and therefore difficult to manufacture synthetically, plants are used as sources of precursors.

Dioscorea - Yams - produce saponins (diosgenin) which are extracted from tubers. These compounds are similar to human sex hormones. Used in birth control pills, fertility drugs, female hormones, cortisone and hydrocortisone.

Diosgenin

Digitalis purpurea - Digitoxin- affects heart muscle by changing rhythmn of beat so that systolic contraction is lengthened, referred to as a cardiac glycoside.

Alkaloids are N-containing compounds which are found in a wide array of plants. They are produced by a number of biochemical pathways, a number of them are produced from amino acids.

Quinine - Cinchona officinalis (Rubiaceae) is used to treat malaria. It was synthesized in 1944 but strains of Plasmodium, the sporozoan which causes malaria, have developed resistance to the synthetic quinine. However, natural quinine is still effective so interest in the plants has been renewed. Quinidine is another product of this plant which is used to control heart problems. Gin and tonic.

Ephedrine - Ephedra sinica (Gymnosperm), used as a decongestant

Cocaine - Erythroxylum coca - S.A. Andes, used as calmative and local anesthetic. A synthetic form called Novocain is similar and has replaced cocaine as a local anesthetic.

Opium - Papaver somniferum (Papaveraceae), one of oldest pain-relieving drugs, native to Eastern Europe and W. Asia. Opium latex is harvested by scoring capsule, allowing it to dry and then collecting dried resin, this process can be repeated many times. There are 26 alkaloids known to occur in Opium latex, most important ones are morphine, codeine, and papaverine.

Morphine - most abundant, potent pain killer, addictive. Heroin is synthesized from morphine.

Codeine - less potent than morphine, non-habit forming, used in prescription and non-prescription pain killers.

Papaverine - used to control internal spasms
Tropane alkaloids - Most are obtained from Atropa belladona (Solanaceae). Belladonna means beautiful lady, drops from an extract of this plant expand pupils, resulting in a wide-eyed, innocent look. The major compounds are atropine and scopalamine, which are used to control smooth muscle spasms - cardiac medicines, pupil dilators, stomach and bladder cramps

Veratrum viride (Liliaceae) produces a number of alkaloids used to treat heart disease, alkaloids are extracted from roots.

Resperine - Rauvolfia serpentina - snakeroot, alkaloids are used in treating hypertension, mental illness, compound is extracted from roots.

Vinblastine and leurocristine - Catharanthus roseus - used for some forms of leukemia, Hodgkin's disease.

Podophyllum peltatum - Mayapple - alkaloids used for treatment of lymphocytic leukemia.

Chaulmoogra oil - Hydnocarpus - treatment of leprosy

Salacin - Salix alba - aspirin (acetylsalicylic acid) is derivative of salicin.

Psyllium - Plantago - a colloidal mucliage used for constipation and diarrhea.

Aloe gel - Aloe barbadensis - aloe gel is used in shampoos, lotions, burn remedies.

Ipecac syrup - Cephaelis ipecacuanha - induces vomiting

Chymopapain - Carica papaya - enzyme used for treatment of slipped disks; injected near region of disk slippage and dissolves cartilage and relieves pressure.

There is currently much investigation into new medicinal uses for plants. Herbal medicine has been practiced in China for thousands of years and is still very important. "Primitive" cultures are being investigated for their uses of plant materials. It is often difficult to distinguish authentic cures from "magic" cures.

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