[muawiyah]

Could also have something to do with a shift away from foreign sources to American producers in that year.

[Ken H]

So the Americans are even better at shielding their crop from low potency strains!

Here are the reported THC figures for "sinsemilla" and "marijuana" respectively from 1989 (the year the WOD became a cabinet level priority), and 15 years later:

1989- 6.95 and 3.04
2004- 13.33 and 5.81

That probably outperformed the gains in John Walters' stock portfolio.