天然产物作为抗癌药的主要来源：

Thus, in the area of cancer, over the time frame from around the 1940s to date, of the 175 small molecules, 131 or 74.8% are other than “S” (synthetic), with 85 or 48.6% actually being either natural products or directly derived there from.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3721181/

The chart below is for all drugs:

Major Categories of Sources

The major categories used are as follows:

• “B” Biological; usually a large (>45 residues) peptide or protein either isolated from an organism/cell line or produced by biotechnological means in a surrogate host.
• “N” Natural product.
• “NB” Natural product “Botanical” (in general these have been recently approved).
• “ND” Derived from a natural product and is usually a semi-synthetic modification.
• “S” Totally synthetic drug, often found by random screening/modification of an existing agent.
• “S*” Made by total synthesis, but the pharmacophore is/was from a natural product.
• “V” Vaccine.