The present invention provides new use and product for treatment of diseases and disease conditions. More particularly, the present invention relates to the new use of bioactive compound derived from the eurycoma longifolia jack for the treatment of obesity and obesity-related diseases. The bioactive compound comprises quassinoid, 13(21)-epoxyeurycomanone. This bioactive compound possesses activity of down-regulating the expression of specific protein that is over-expressed on blood vessel cells that serve only white fat tissue but absent on blood vessel cells of other tissues or organs. Therefore, the bioactive compound has the effects on inhibition or reduction of the formation of blood vessels in white fat tissue and eventually reverses the obesity and eventually obesity-related diseases.