"In July 2017, police forces from several countries worked together to take down the largest drug-trading platform on the darknet, the part of the “deep web” containing information that is only accessible using special web browsers. Before it was closed, AlphaBay had featured more than 250,000 listings for illegal drugs and chemicals. It had had over 200,000 users and 40,000 vendors during its existence. The authorities also succeeded in taking down the trading platform Hansa, described as the third largest criminal marketplace on the dark web.

"Objective: To examine the effect on the trade in opioids through online illicit markets (“cryptomarkets”) of the US Drug Enforcement Administration’s ruling in 2014 to reschedule hydrocodone combination products.

"Design: Interrupted time series analysis.

"Setting: 31 of the world’s largest cryptomarkets operating from October 2013 to July 2016.

"The internet has facilitated the sale of licit and illicit drugs for more than 15 years,^{10 11 12 13} but when the first cryptomarket, Silk Road ¹, came online in 2011, illicit drugs began to be traded in large quantities. The annual turnover of drug sales conducted through cryptomarkets is estimated to be in the hundreds of millions of dollars,¹⁴ with most transactions involving recreational drugs (eg, cannabis, “ecstasy”).

"The US Drug Enforcement Administration introduced a schedule change for hydrocodone combination products in October 2014. During the period of our study, October 2013 to July 2016, the percentage of total drug sales represented by prescription opioids in the US doubled from 6.7% to 13.7%, which corresponds to a yearly increase of 4 percentage points in market share. It is not possible to determine the location of buyers from cryptomarket data. We cannot know, for example, if a drug shipped from a vendor in Europe was purchased by a US customer.