An inhibitor of ghrelin de-acylation (GDAi) such as an APT1 inhibitor for use in the treatment or prophylaxis of physiological or pathophysiologicial conditions that are mediated by acylated ghrelin (AG) and un-acylated ghrelin (UAG) in mammals. Such conditions include CNS disorders such as Alzheimer's disease and Parkinson's disease. Peripheral administration of the inhibitors is a useful method of treatment for such conditions. Also, the ratio of AG to UAG (as well as the GDA enzyme content or GDA enzyme activity) can be a useful biomarker that may be used as the basis of diagnostic techniques.
