The French health ministry issued a warning on Tuesday after eight people died and seven fell sick in two European countries from using heroin contaminated by anthrax.
"Since December 6, there have been 15 confirmed cases of anthrax among heroin users, 14 in Scotland and one in Germany," the ministry's General Directorate for Health (DGS) said in a statement.
"Eight people died," it said. "The likeliest source is heroin contaminated by anthrax spores."
Most of the casualties had injected the heroin, but others also inhaled it or smoked it.
Anthrax is a potentially lethal bacterium that exists naturally in the soil and can also occur among cattle. It is also, more notoriously, a potential bio-terror weapon.
The ministry said the contaminated drug may also be circulating in France and other European countries.
"There is no outward sign or colour enabling the user to tell whether the heroin has been contaminated by anthrax, and contaminated heroin dissolves or is used in the same way as uncontaminated heroin," it said.