There are more people using methamphetamine worldwide than users of heroin and cocaine combined, according to U.S. Drug Enforcement Administration (DEA) head Karen Tandy.

The BBC reported May 10 that Tandy, speaking at the 24th International Drug Enforcement Conference in Montreal, described meth use and trafficking as a growing "global threat."

"More than 26 million people worldwide use amphetamines -- largely methamphetamines," she said.

Some experts said that growing meth use could lead to a worldwide increase in related crime. "We know that many of the people that are arrested in Los Angeles -- about 40 percent of them -- have been using methamphetamine," said California-based neuroscientist Paul Thompson. "We're worried that as this drug is spreading throughout the US and overseas, this could produce a massive increase in violent crime."