The use of mood enhancing drugs such as amphetamine and ecstasy are now prevalent in society. These compounds are known to produce serious psychological and physiological problems in users, which can, in some circumstances result in death. While there has been much research into the effects of these drugs on the body, little if any research has investigated the effect of the side products and synthetic reaction by-products which are a consequence of there illegal production. In the study the effects of nitrostyrene, a reaction by-product in one of the routes to synthesis of amphetamine sulphate, on cell viability and macrophage function was determined. Treatment with nitrostyrene at doses > 0.75 µg/mL had a significant suppressive effect on the proliferation of stomach cancer lines. Treatment of macrophages with doses as high as 10 µg/mL did not effect cell viability. Nitrostyrene treatment of macrophages, stimulated with IFN ? and LPS, resulted in a dose dependent differential inhibition in IL12, IL6 and nitrite production, even using doses <0.5 µg/mL. Thus ranking of the three, on the basis of the suppressive effect obtained, is IL12 > nitrite > IL6. Thus ingestion of nitrostyrene contaminated ecstasy is likely to have a adverse effect on the immune responses of the recreational user.