The sympathetic nervous system (SNS) is hyperactive in women with polycystic ovary syndrome (PCOS). This study was designed in two sections: in vivo/in vitro with clonidine as the alpha-2 adrenoceptor (ADR-α2) agonist for modulating this hyperactivity. Eighty women with PCO participated in this randomised clinical trial (in vivo). A clonidine (0.1 mg) tablet was given twice a day for two months. Polycystic ovary morphology (PCOM) and pregnancy rate were the main outcome measurements. In the candidates for in vitro fertilisation (IVF), clonidine was added to the culture medium during IVF for two study groups (PCO-clonidine/PCO-without) and two control groups (egg donors-clonidine/egg donors-without). Our results showed that the pregnancy rate significantly was higher in the study group (p = .002). The mRNA expression of ADR-α1 and ADR-β2 in PCO was higher than control group (p value