The streets of San Francisco are awash with a new drug called ISO that’s twenty times more potent than deadly fentanyl – and officials are sounding the alarm. The killer counterfeit opioid isotonitazene – known on the streets as ISO – claimed its first life in the drug-ravaged city in April, San Francisco Health Department officials said in an alert issued that month. San Francisco health officials said ISO was blended with another synthetic opioid called cychlorphine in the overdose death