The Red Cross said five patients at a Mexican drug rehabilitation clinic died after eating contaminated soy sausage as a Christmas meal, the BBC reported.
An additional 37 patients were taken to the hospital for dizziness and nausea, and several of them are in serious condition.
Authorities are investigating whether the contamination was intentional. Drug gangs have often targeted rehab clinics over the years.
“I do not know if it was intentional or whether it was human error,” said Daniel Nunez, spokesman for the Red Cross.
Nunez said authorities are looking into the possibility of cyanide poisoning.