"A primary activity of supply-control programs is seizing cocaine. This, however, does not directly decrease the supply of cocaine reaching the retail market. Free entry into the cocaine business, at all levels, allows supply to expand to cover the losses due to seizures.8 To a first-order approximation, suppliers simply produce for the market what they would have produced anyway plus enough extra to cover anticipated government seizures."
Source
Rydell, C.P. & Everingham, S.S., Controlling Cocaine. Drug Policy Research Center, RAND, 1994. Prepared for the Office of National Drug Control Policy and the United States Army.