The businesses in question allegedly sold around four tons of ephedrine between 2006 and 2011 to Mexican national Ezio Figueroa Vásquez, or enough to produce 66 million methamphetamine capsules worth roughly $370 million, according to AFP. 

In 2012, the US Treasury Department designated Vásquez as an international drug trafficker under its "Kingpin Act." Treasury described him as leading "an international precursor chemical trafficking organization responsible for the diversion and importation of multi-ton quantities of pseudoephedrine and ephedrine from Europe and sub-Saharan Africa into Mexico." Vásquez then sold the chemicals to Mexican drug trafficking organizations to manufacture methamphetamine.

According to Proceso, the US Drug Enforcement Administration linked Vásquez directly to incarcerated Sinaloa Cartel leader Joaquín "El Chapo" Guzmán. Mexican authorities arrested Vásquez in 2011.

Identities of the implicated companies and executives were not confirmed by Belgian authorities. Belgian pharmaceutical group Sterop, however, admitted it was part of the case, but claimed it had been deceived by intermediaries and committed no crime.

A Belgian court will decide on April 5 whether the case should go to trial.

InSight Crime Analysis

This case stands out because of where the precursor chemicals were coming from. Precursors like ephedrine are essential to methamphetamine production, but they have become increasingly difficult to procure as governments in the region tighten legal restrictions on their sale and distribution.

Due to its lax regulations, China has become a major precursor chemical source for Mexican drug trafficking organizations, and authorities have interdicted multi-ton shipments of Chinese precursors entering Mexico's Pacific ports. In 2014, Mexican authorities sentenced a top Chinese-Mexican methamphetamine trafficker, who helped cultivate the Sinaloa Cartel's connections in Asia, to 25 years in prison.

In recent years, lax oversight of Argentina's pharmaceutical industry has converted the South American nation into another key source of precursors for Mexican groups.

Until now there has been scant evidence, however, of European nations directly supplying precursor chemicals to Mexican drug organizations. While the case involving the Belgian pharmaceutical companies is troubling, it is unlikely part of a wider trend, as the European Union has detailed regulations in place to control the trade of precursor chemicals.