They are natural, semisynthetic, and synthetic. Natural resources are plants, animals, minerals, microorganisms, etc. Semisynthetic drugs are obtained from natural sources and are chemically modified later. Synthetic drugs are produced artificially. The different sources of drugs are:
i. Alkaloids, e.g. morphine, atropine, quinine, reserpine, ephedrine.
ii. Glycosides, e.g. digoxin, digitoxin.
b. Animals: Insulin, heparin.
c. Minerals: Ferrous sulphate, magnesium sulphate.
d. Microorganisms: Penicillin, streptomycin, griseofulvin.
e. Semisynthetic: Hydromorphone, hydrocodone.
f. Synthetic: Most of the drugs used today are synthetic, e.g. aspirin, paracetamol.
* Drugs are also produced by genetic engineering (DNA recombinant technology), e.g. human insulin, human growth hormone, hepatitis B vaccine.