Carboxy-THC is the primary metabolite of THC, a key indicator of marijuana usage. In urine, about 80% of the carboxy-THC metabolite is present in the form of its glucuronide metabolite. Therefore, to effectively quantify the THC-COOH using GC-MS, urine is hydrolyzed before extraction. This application note describes optimized supported liquid extraction of urine samples prepared by either enzymatic or base hydrolysis, and provides a brief summary of the pros and cons of each hydrolysis approach. The simple sample preparation procedure delivers clean extracts and analyte recoveries greater than 87% with RSDs lower than 10% for all analytes, and is optimized for use with 1 mL sample capacity ISOLUTE® SLE+ columns.