"Based on the inputs and the calculations explained above, the value of the global illicit drug market for the year 2003 was estimated at US$13 bn [billion] at the production level, at $94 bn at the wholesale level (taking seizures into account), and at US$322bn based on retail prices and taking seizures and other losses into account. This indicates that despite seizures and losses, the value of the drugs increase substantially as they move from producer to consumer.
"The largest market, according to these estimates, is cannabis herb (with a retail market size of $113 bn), followed by cocaine (US$71 bn), the opiates (US$65bn) and cannabis resin (US$29 bn). The ATS markets together (methamphetamine, amphetamine and ecstasy) amount to US$44 bn. The valuation does not take into account the value of other drugs."
United Nations Office on Drugs and Crime (UNODC), World Drug Report 2005 (Vienna, Austria: UNODC, June 2005), p. 127.