For centuries, drugs were entirely of natural origin
and composed of herbs, animal products, and inorganic
materials. Early remedies may have combined these ingredients
with witchcraft, mysticism, astrology, or religion,
but it is certain that those treatments that were effective
were subsequently recorded and documented, thus leading
to the early Herbals. The science of pharmacognosy – the
knowledge of drugs – grew from these records to provide
a disciplined, scientific description of natural materials
used in medicine. Herbs formed the bulk of
these remedies. As chemical techniques improved, the
active constituents were isolated from plants, were structurally
characterized, and, in due course, many were
synthesized in the laboratory. Sometimes, more active,
better-tolerated drugs were produced by chemical modifications
(semi-synthesis), or by total synthesis of analogues
of the active principles.