You smoked weed 20 days ago will you pass a drug test?

If it was incidental use, it would clear within 48 to 72 hours. If it was repetitive use, it will persist longer, even for weeks and months. Some tests are not as accurate.

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Look into some of the legitimate legal highs, there are some out there that really work just like THC and test clean. Basically they're simple chemicals that mimic THC's effects on the brain because they have the same receptor bonding surfaces, but a different overall chemical architecture.