GR-113,808 is a drug which acts as a potent and selective 5-HT₄ serotonin

Serotonin

Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...

 receptor

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

 antagonist

Antagonist

An antagonist is a character, group of characters, or institution, that represents the opposition against which the protagonist must contend...

. It is used in researching the roles of 5-HT₄ receptors in various processes, and has been used to test some of the proposed therapeutic effects of selective 5-HT₄ agonists, such as for instance blocking the nootropic

Nootropic

Nootropics , also referred to as smart drugs, brain steroids, memory enhancers, cognitive enhancers, and intelligence enhancers, are drugs, supplements, nutraceuticals, and functional foods that improve mental functions such as cognition, memory, intelligence, motivation, attention, and concentration...

 effects of 5-HT₄ agonists, and worsening the respiratory depression produced by opioid

Opioid

An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

analgesic drugs, which appears to be partly 5-HT₄ mediated and can be counteracted by certain 5-HT₄ agonists.