The act of prescribing pharmaceutical drugs to patients is normally the site of judgements about the drug's efficacy and safety. The success of treatments and the licences for commodities depend on the biochemical identity of the drugs and of their path and transformations inside the body. However, the 'supply chain' outside the body is eschewed by such discourse, and its importance for both pharmaceutical brands and physician-centred historiographies is ignored. As this ethnographic fieldwork on Tibetan and Chinese medicines in Sichuan shows, overlooked social actors ensure reliable knowledge about medicinal things and materials long before patients take their medicine. This paper takes a step back from the final products-clearly defined as 'Tibetan' or 'Chinese'-and introduces those who produce and distribute them. Via observations of particular regimes of circulation and processing, the actions of collecting, manufacturing, transporting, and educating appear as the first and foremost acts of efficacy and safety.;