Now, my character is a recovered drug addict (cocaine and morphine). She's been clean for about a year. Then for reasons that would take way too long to get into, she decides to take a decent-sized dose of cocaine. A short time later, she runs afoul of a forest fire and has to be treated for smoke inhalation and burns. She's treated by a doctor who knows her her history. The doctor runs some tests on her blood and discovers that my character used cocaine recently. I need it to know what the soonest after my character used cocaine it would be safe for her to take hardcore painkillers. I know that because of my character's history of abusing morphine, the doctor would be reluctant to prescribe narcotics, but I'm handwaving it by saying that she's just in that much pain.
Setting is US in about fifty years.