TEHRAN — Sitting on one of the many crowded benches in the waiting room of the International Red Crescent’s pharmacy in central Tehran, Ali, 26, was working his phone. After nearly six weeks of chasing down batches of Herceptin, an American-made cancer medicine, Ali, an engineer, was wearing out his welcome with friends and relatives in other Iranian cities, who had done all they could to rustle up the increasingly elusive drug.

At home his mother waited, bald and frail after chemotherapy for her breast cancer, but Herceptin had disappeared from pharmacies and hospitals in the capital.

“So you are telling me that a pharmacy in Qazvin has 20 batches left?” Ali asked, talking about a city two hours’ drive east of Tehran. “Please buy whatever you can get your hands on.”

But five minutes later bad news came: “Gone? O.K., thank you for your troubles. If you do find some please call me by the soonest.”