The present invention relates to methods and pharmaceutical compositions for treating obesity or obesity-related disorders in a subject suffering from or predisposed to developing obesity or an obesity-related disorder, or for inhibiting the infectivity of HIV, by administering oleuropein, an analogue or derivative thereof, or the major metabolites of oleuropein including oleuropein aglycone, hydroxytyrosol, and elenolic acid or their analogues, or derivatives thereof, an iridoid glycoside, or a secoiridoid glycoside or analogues or derivatives thereof, or any combination of the foregoing including olive leave extract. The invention also relates to methods for screening/diagnosing a subject having, or predisposed to having obesity or a related disorder by measuring the expression profiles of an adipogenic gene selected from PPARγ2, LPL and αP2 gene and gene product, or other adipogenic, lipogenic, or lipolytic genes and gene products in an individual. The invention further provides for screening for novel oleuropein analogues.