The targets for drugs (ligands) can roughly be divided into two groups. The first group includes human cellular drug targets i.e. proteins and nucleic acids. Proteins are by far the most important targets for drugs. Receptors, enzymes, ion channels and transporters all belong to the group of proteins and will be discussed in detail. Nucleic acids are targets for anticancer drugs (see chapter oncology).
The second group is diverse and contains non-human targets such as chemical drug targets (such as ions and surfactants) and drugs without a receptor (laxatives) and drug targets on microorganisms. In infectious diseases the drugs bind to receptors on the infecting agents in order to inhibit their growth or to destroy these. More information about anti-microbial drugs can be found in the chapter of infectious diseases.