Drug dealers looking for extra profits apparently added lead flakes to packets of marijuana, inflating their value while causing dozens of cases of serious poisoning, doctors in Germany have reported.
The lead made up, on average, 10 per cent of the material in the marijuana packets, boosting profits by about $US1500 ($NZ1900) per kilogram, Franzika Busse of University Hospital Leipzig reported.
"One package contained obvious lead particles; this strongly indicated that the lead was deliberately added to the package rather than inadvertently incorporated into the marijuana plants from contaminated soil," the researchers wrote in a letter to the New England Journal of Medicine.
The problem was discovered last year when the first of 29 patients, aged 16 to 33, started showing up in four Leipzig hospitals with abdominal cramps, fatigue, nausea and varying degrees of anemia. One was ill enough to be suffering from hallucinations.
It took eight weeks to uncover a common pattern: all were young, smoked, had body piercings and were either students or unemployed. All regularly used marijuana.
Three patients brought in their stashes. All samples tested positive for lead contamination, with one having lead flakes that were obvious under a microscope.
After two more weeks, an anonymous screening programme for marijuana users uncovered 95 other people who needed treatment.
Busse's colleague, Dr Michael Stumvoll, said in an e-mail that about 200 people have now been identified. The screening is continuing, he said, although it does not appear that the practice is continuing among dealers.
"The medical community, including pediatricians, should consider adulterated marijuana as a potential source of lead intoxication," the German team wrote.