One theory explaining the upsurge in popularity of Colombian heroin is the 10-year cycle. This theory claims that about every 10 years a new drug takes the lead in popularity and the previous one loses its popularity. The article also examines combination heroin/cocaine use and addiction, taking heroin to soften and prolong the effects of crack cocaine, and heroin’s increased purity, increased social acceptance and decreased social stigma because it is feasible to administer it by means other than the hypodermic needle. Supply-side factors include Colombian marketing practices (providing heroin free to cocaine purchasers, knowing that the buyer will become dependent on the heroin and be a future customer); undercutting the heroin market in price; and providing a high-purity product. The article also discusses Colombia’s convenient geographical position as a factor in the country’s pre-eminence in the U.S. heroin market. Notes