Table 3. chronological data of the natural product leads with the first approved drugs and the drug lead productive clusters during every five-year period from 1963 to 2012. The six drug lead clusters with only one approved drug plus one or more clinical trial drugs were not included here.

	Number of natural product leads with the first approved drug in period		Number of drug lead clusters in period
Period	Inside preexisting DCs	Outside preexisting DCs	Number of preexisting DCs	Number of new DCs
Pre–1963	56	NA	8	NA
1963–1967	7	20	8	7
1968–1972	4	9	15	3
1973–1977	9	8	18	2
1978–1982	17	56	20	13
1983–1987	20	20	33	5
1988–1992	20	12	38	6
1993–1997	20	9	44	2
1998–2002	19	10	46	3
2003–2007	9	6	49	1
2008–2012	11	6	50	4