He recently received an A-rating from the National Research Foundation.

His research focuses on the neuroendocrinology of reproduction. This addresses the mechanisms by which diverse internal factors (e.g. sex hormones, stress hormones, infection, glucose, lipids and other metabolites) and external factors (e.g. day length, temperature, stress, chemicals and foods) signal to the brain which then integrates this information to regulate reproduction. For example, nutritional deprivation as in anorexia nervosa and the loss of menstrual cycles due to weight loss in long distance runners result from a reduction in the brain hormone gonadotropin-releasing-hormone (GnRH).

Prof Millar is a pioneer in research on GnRH and its receptor which has led to the development of a billion dollar market in GnRH drugs for the treatment of a range of diseases such as prostatic and other cancers, as well as endometriosis and polycystic ovarian disease which afflict up to 30% of women.
 

Although it was clear the GnRH was a master brain hormone controlling reproduction we had no idea how the diverse factors mentioned above regulated the GnRH neuron as it lacked receptors for the regulators. This conundrum was recently solved by the discovery that mutations in genes encoding two brain hormones and their receptors led to a failure in humans to progress through puberty. The hormones, Kisspeptin and Neurokinin B are now a major focus of research directed at developing new drugs for treating diseases of human reproductive tissues.

He contributed to these advances in many publications including two recently published in the prestigious New England Journal of Medicine. These articles described mutations in the human GnRH gene and Kisspeptin gene which result in a failure to advance through puberty.
 

Prof Millar is now using this clinical knowledge to understand how environmental stresses such as food deprivation, infection (e.g. TB) and high temperatures resulting from climate change impinge on the neuroendocrine system to affect reproduction in wildlife, and how responses to Kisspeptin and Neurokinin B are a sensitive index of stress and disease.