The term "biological target" is frequently used in pharmaceutical research to describe the native protein in the body whose activity is modified by a drug resulting in a specific effect, which may be a desirable therapeutic effect or an unwanted adverse effect.  In this context, the biological target is often referred to as a drug target. The most common drug targets of currently marketed drugs include:
* proteins
** G protein-coupled receptors  (target of 50% of drugs)
** enzymes (especially protein kinases, proteases, esterases, and phosphatases)
** ion channels
*** ligand-gated ion channels
*** voltage-gated ion channels
** nuclear hormone receptors
** structural proteins such as tubulin
** membrane transport proteins
* nucleic acids