It is possible that such results occur because CB1 receptors are not effectively blocked and that only a complete blockade of CB1 receptors in a given situation may determine the role of CB1 antagonists, for example, the use of CB1 receptor antagonists at low doses in moderate PD or when PD progresses to an advanced stage (Fernandez-Espejo et al., 2005; Gonzalez et al., 2006). This evidence concerns the gene CNR1 and Parkinson disease.