Mexico said on Thursday it has made the biggest seizure of pure fentanyl in its history, after five suspected drug traffickers were arrested at a lab along with 118 kilograms of the synthetic opioid. Fentanyl is 50 times more potent than heroin, and only a tiny amount is needed to make counterfeit oxycodone pills. The Mexican army said the lab, busted on October 28 in the northern city of Culiacan, probably made about 70 million of the blue fentanyl pills every month for the Sinaloa cartel. “This seizure of pure fentanyl is considered the largest in history,” the defence department said. The lab and the warehouses used to store precursor chemicals to make fentanyl stretched over five buildings. Most of the chemicals are imported from abroad, usually China or India. The suspected ringleader of the operation and four of his accomplices have been held pending trial. Known as “Mexican oxy,” the counterfeit pills are so poorly manufactured that some contain almost no fentanyl, while others contain a lethal dose. Opioid overdose deaths in the United States reached about 50,000 in 2019, with most of those attributable to synthetic opioids. The Mexican army's seizure of fentanyl and methamphetamines had nose-dived in recent months before the October 28 bust was announced.