Selective estrogen receptor modulators (SERMs) are compounds that act on the estrogen receptors (ERs). A characteristic that distinguishes these substances from pure ER antagonists and agonists (silent antagonists and full agonists) is that their action is different in various tissues, thereby granting the possibility to selectively inhibit or stimulate estrogen-like action in various tissues.

Transporters are proteins that span the plasma membrane and regulate the traffic of small molecules in and out of the cell. They play a particularly important role in chemical signalling between neurons in the CNS, where they act to control the concentration of neurotransmitters in the synapse. Another key role for transporters is in excluding undesirable xenobiotics from the cell, whilst allowing key molecules required for the cell life cycle to enter. The majority of transporters are targets for drug discovery.