How long can weed remain in your system?

Cannabis: Single use marijuana may be found in blood for 12 to 24 hours. Regular use marijuana may be found in blood for 2 to 7 days. Single use marijuana might be detected in urine for 1 to 7 days (or more) and regular marijuana can be detected in urine for 7 to 100 days (longer periods have been reported though). Regular use cannabis may be found in hair for months.