It's gonna take time. A whole lot of precious time.
Gerhart is a responsible professional whose job is to not enable drug addicts. He emphasized the techniques that don't work and peppered his cautionary tales with annoyingly wise rhetorical questions (e.g., "Why is it so important for you to be high?"). He says the only surefire way to pass a drug test is to actually lay off drugs for a while.
"The thing that gets someone clean enough to pass the test is time," he says. "Typically, stimulant-type drugs have a shorter half-life -- they're out of your system in days. Cannabis can take weeks or months depending on the quantity, quality, and that person's condition."
Someone who's heavyset, not physically active, and who's regularly smoking the finest medical-grade sativa is going to have marijuana metabolites in their system for up to 90 days after quitting, Gerhart says. So logically, if you're a skinny marathon runner who only tokes up every few weeks or so, your time to pass a drug test will veer toward the lower end of that spectrum.
California NORML breaks down the average time it takes to clear popular drugs, though it's worth reiterating that everyone processes substances differently. For a single use of marijuana, you can bet on anywhere from a day to a week or more before your urine's clean. Heavy users might need up to three or more months. For speed, coke, heroin, and other opiates, you're looking at one to four days. PCP is going to stay in your system for three to seven days, and for all of the above, a hair test might return a positive result for months after the last time you used.