In Germany a consumer of controlled substances is regarded as unfit to drive motor vehicles. The Road Traffic Licensing Board has to revoke the license from consumers of controlled substances. A re-granting is considered only if the applicant can prove that he does no more consume such agents. But cannabis takes an exceptional position because a consumer of cannabinoids is regarded as unfit to drive motor vehicles if only a habitual consumption is to be assumed. In the cases of an occasional consumption, separation of consumption and driving, no additional taking of alcohol and other drugs, and in the absence of a disturbed personality or loss of control the aptitude for driving a motor vehicle is not considered to be impaired. In much cases of testing for cannabinoids not only consumption is to be stated but also information about frequency of consumption shall be given. Urine is a useful material for drug testing. But urine samples can be manipulated not only by drinking high amounts of water. If information about the frequency of consumption is necessary, blood should be analysed because the concentration of the THC-metabolite in urine depends not only on the concentration in blood and the creatinine content but also on other factors.