How long can THC metabolites be detected in urine?
(Ellis and colleagues):
The urinary excretion patterns of 86 chronic cannabis users were examined after their last cannabis use by two common screening methods (...). We demonstrated that under very strictly supervised abstinence, chronic users can have positive results for cannabinoids in urine (...) for as many as 46 consecutive days from admission, and can take as many as 77 days to drop below the cut-off calibrator for 10 consecutive days. For all subjects, the mean excretion time was 27 days (...). Demographic, body type, and drug history variables proved to be only moderate predictors of excretion patterns."
Ellis GM Jr Mann MA Judson BA Schramm NT Tashchian A. Excretion patterns of cannabinoid metabolites after last use in a group of chronic users. Clin Pharmacol Ther 1985;38(5):572-578.
Excretion of THC and its metabolites in chronic users can be found in the range of 4-6 weeks. In the literature a 10 year long intensive cannabis use was reported to result in detection of use after 77 days with common tests. With single or occasional use excretion in urine is rarely short (some hours), usually it lasts for 3-5 days.
Aderjahn R. Toxikologischer Cannabisnachweis [Toxicological cannabis detection]. In: In: Berghaus G, Krüger HP, eds. Cannabis im Straßenverkehr [Cannabis in road traffic]. Stuttgart: Gustav Fischer, 1998.
(Coleman en Baselt):
OBJECTIVE: We have become aware of several commercial products that, when orally ingested, will purportedly not only eliminate "toxins" from a person's system, but will also correct any urinary imbalances caused by excessive water consumption. METHOD: Unblinded study of one volunteer subject, tested weekly x 4 for 24-hour urine elimination of test drug under conditions of control, control plus 1200 ml water, Quick Flush, and Eliminator. RESULTS: Each of the treatment protocols studied caused reductions of drug or metabolite concentrations as measured by gas chromatography-mass spectrometry in urine specimens (...), yet the radioimmunoassay screening results demonstrated very little effect. Water alone was approximately as effective as the two commercial products in reducing the metabolite level. None of the treatment protocols employed in this study altered urinary pH, specific gravity, or creatinine concentration outside the normally accepted physiological range. CONCLUSIONS: Attempts to conceal drug abuse by water dilution are most likely to play a substantial role when concentrations are at or near the detection threshold for a particular assay such as the terminal stages of drug eliminations. Coleman DE Baselt RC. Efficacy of two commercial products for altering urine drug test results. J Toxicol Clin Toxicol (1997) 35(6):637-642.
The commercial urine cleaner are relatively reliable, if one follows the instructions for use. But these products should only be tried if it is urgent. If there are several weeks of time it is sufficient to drink much (about three litres a day), do much exercise, take vitamins as well as sweat much. However, with this amount of fluids the concentration of creatinine (degradation product of creatine that is also tested) is lowered. This can be prevented by starting to take a creatine preparation from the pharmacy some days before the test.