text: 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