Niacin does not flush THC, the active ingredient of cannabis, from the body. It is ineffective as a mask for marijuana use and can be dangerous at the levels recommended for beating an upcoming drug screen, according to Emergency Medical News and The Journal of Clinical Toxicology.
As of 2013, two cases of liver dysfunction due to overdosing on niacin to beat a drug screen have been reported, states The Journal of Clinical Toxicology. In both cases, the young men found information on the Internet instructing them to ingest large quantities of the nutrient to avoid testing positive for marijuana. In both cases, the patients ended up in the hospital reporting nausea, vomiting and stomach pain. They also both tested positive for THC. The only reliable way to beat a drug test is to stop taking drugs.