Not long. Especially compared to THC. For example, a urine test will detect THC in first-time marijuana users about three days after use. For weekly smokers, that will be more like five days. And for daily smokers, a urine test can detect THC around 30 days after the last use. If you only use CBD or full-spectrum hemp oil, though, the THC will leave your system much faster since there’s so much less of it.