Emma remembers the first time she took one of the pearly white oblong pills, like straightened-out Polo mints with X-A-N-A-X indented along one side. They felt cool and light, and rattled like beads in her palm.

“Me and my friends thought it would be really funny if we took them during lessons at college,” she says. “Which is probably the most 16-year-old thing ever.”

The counterfeit pills split into quarters, and Emma snapped one along its indentations, to make four tiny cubes that scattered across the desk like dice. One by one, she and her friends swallowed the letters. Then they did it a second time. “We didn’t feel anything straightaway, so obviously we thought we should just take more,” she says.

Emma felt an