Despite the legalization of recreational and medicinal marijuana in California, employers maintain the right to enforce a drug-free work environment. In many respects, cannabis is now treated like alcohol; although consumption of alcohol is legal for those over the age of 21, employers may prohibit drinking during work hours and discipline any employee who comes to work intoxicated. But regulation of cannabis in the workplace differs from alcohol because testing for THC, the compound in marijuana that gets you high, is not like testing for alcohol. Unlike tests for alcohol that measure current impairment levels, there is no test that will reveal whether an individual is currently high. In fact, a regular user may test positive for marijuana weeks after the individual last used. So when may employers test employees for marijuana?