The use of illicit drugs in the workplace raises issues pertaining to prevention and safety and the responsibility of the various members of staff. It also brings into question the interface between work and private life. If employees are in theory responsible for their own safety and risk heavy penalties in the event of the consumption of illicit drugs in the workplace, such behaviour has to be proved. In reality, the worker can only be partially and marginally held liable, given the fact that the employer is prohibited from infringing on their rights and liberties (restrictions on the searching of their personal belongings and lockers as well as on the carrying out of breath testing and saliva testing under restrictive conditions). Employers have for their part a broader range of responsibilities and, above all, an absolute obligation to achieve specific goals in terms of health and safety resulting in the need to take action. In accordance with the International Labour Organization recommendations, European and national legislation, the employer has to implement a suitable preventive policy. However, where is the balance between prevention and repression? Very few studies have raised these issues and our aim is to precisely situate the place of drug testing in the employer's repressive arsenal in France and to try to answer the legal and ethical issues raised. Thus, for example, repression can only be acceptable when it deals with moderate and non-addicted users, or it could be tantamount to discrimination.