The crux of pharmacology: how a drug actually works in your system. Researchers investigate, for instance, how the drug’s molecular shape can affect its power.  

The study of how a medication is absorbed, processed and eventually eliminated by the body. Labs can determine a drug’s half-life (how long it takes for the body to excrete half of the drug) and its Cmax (the maximum concentration it reaches). These measures determine the size and frequency of an HIV med’s dosing.

Your genes can wildly alter the way a drug affects you (see “Meet Your Host,” POZ, November 2004). Pharmacogeneticists try to identify how different people respond to drugs (more side effects in one person, longer half-life in another) and probe their genes for the cause.