Today natural products and their derivatives represent about 50% of all drugs in clinical use with higher plant-derived natural products representing approximately 25% of the total.

In a review article, Newman et al from the National Cancer Institute pointed out that from 1982 to 2002, approximately 28% of the new chemical entities in western medicine were either natural products per se or derived from natural products. Thus of 1,031 new chemical entities over this 22-year period, 5% were unmodified natural products, and 23% were semi-synthetic agents based on natural product lead compounds. An additional 14% of the synthetic compounds were designed based on knowledge of a natural product ‘pharmacophore’.

Further in the 13th revision of the WHO Model List of Essential Medicines, of approximately 300 drugs considered necessary for the practice of medicine, approximately 210 are smaller molecular agents. Of these, more than 40 are unmodified natural products, 25 are semi-synthetic drugs based on natural product prototypes, and more than 70 are either synthetic drugs based on natural product prototype molecules or synthetic mimics of natural products.

Though some plant drugs were replaced by synthetic equivalents, several of them have been studied in recent years to evaluate new uses and/or new dosage forms, providing at least a new therapeutic or investigational impetus in several cases, as can be seen from the examples below:

• Antimalarial quinine is also shown to relieve frequency of nocturnal cramps at an oral dose of 200–300 mg at bedtime.
• Transdermal scopolamine a drug introduced for motion sickness in 1980s is found to be equally effective in the reduction of nausea and vomiting after ear surgery.
• Cannabis sativa is the source herb of psychoactive cannabinoids. New synthetic cannabinoids are under development, which have anti-emetic effects without psychotropic activity.
• Apart from its therapeutic utility in asthma, theophylline is also shown to have anti-inflammatory actions at low serum concentrations of </= 10 mg/L and may also be used in acute life-threatening asthma attacks to reduce the need for mechanical ventilation.
• Though the use of the cinchona alkaloid quinine as an antimalarial declined with introduction of synthetic antimalarial agents such as chloroquine and mefloquine, its use has been re-established due to the widespread emergence of chloroquine-resistant and multiple drug-resistant strains of malarial parasites. It is being considered to be the drug of choice for several chloroquine-resistant malaria due to Plasmodium falciparum.