Progesterone is a hormone released by the corpus luteum – a temporary gland that the female body produces each cycle after ovulation. It plays an important role in the menstrual cycle and is crucial in maintaining the early stages of pregnancy. Progesterone also enhances the effect of the calming neurotransmitter GABA.Hormone Health Network. (n.d.). Progesterone. [online] Available at: https://www.hormone.org/hormones-and-health/hormones/progesterone [Accessed 18 Oct. 2018]. Smith, S.S., Waterhouse, B.D., Chapin, J.K. and Woodward, D.J. (1987). Progesterone alters GABA and glutamate responsiveness: a possible mechanism for its anxiolytic action. Brain research, 400(2), pp.353-359.