The recent introduction of covert administration of treatment to biomedical research has produced some interesting results, with many clinical and ethical implications. Concealed treatment has been used in people with nervous system conditions including pain, anxiety, and Parkinson's disease. The main finding is that when the patient is completely unaware that a treatment is being given, the treatment is less effective than when it is given overtly in accordance with routine medical practice. The difference between open and hidden administrations is thought to represent the placebo component of the treatment, even though no placebo has been given. The decreased effectiveness of hidden treatments indicates that knowledge about a treatment affects outcome and highlights the importance of the patient-provider interaction. In addition, by use of covert administration, the efficacy of some treatments can be assessed without the use of a placebo and associated ethical issues.