"In summary, prices for powder cocaine, crack, and heroin declined sharply in the 1980s and have declined more gradually since then, with periodic interruptions by modest price spikes that have usually persisted for a year or less. For d-methamphetamine, the pattern is broadly similar, but the price spikes appear to be larger and longer-lasting, particularly for 1989–1991. Marijuana prices have followed a very different pattern, increasing from 1981 to 1991, then declining through 2000 and increasing over the past three years."


Office of National Drug Control Policy, "The Price and Purity of Illicit Drugs: 1981 Through the Second Quarter of 2003" (Washington DC: Executive Office of the President, November 2004), Publication Number NCJ 207768, p. vii.