This chapter, Chemical Supplementing, presents ethnographies of young people who use a variety of supplements in order to optimize their health. In the Philippines, boys take multivitamins with the hope of increasing their height, reflecting the importance of stature in their society, and young professionals take expensive supplements to improve their stamina for their demanding distribution jobs in a multilevel marketing company. In fitness centers, young women use proteins and fortified shakes to achieve an idealized, lean, and muscular body. In health and vitamin stores in Amsterdam, growing numbers of young people are buying, sharing, and promoting their personal concoctions of proteins and vitamins. These supplementing practices stem from young people’s various needs: to respond to the demands of service sector labor, to recover from the strain of night work, to indulge in the pleasure of weekend raves, and to manage growing concerns about environmental toxins. By zooming in on supplementing practices of these different groups of young people, we get a clearer understanding of their shared sense of vulnerability, and of the need for better regulation of the supplements industry.