Examples
One notable example of functional selectivity occurs with the 5-HT2A receptor, as well as the 5-HT2C receptor. Serotonin, the main endogenous ligand of 5-HT receptors, is a functionally selective agonist at this receptor, activating phospholipase C (which leads to inositol triphosphate accumulation), but does not activate phospholipase A2, which would result in arachidonic acid signalling. However, the other endogenous compound Dimethyltryptamine activates arachidonic acid signalling at the 5-HT2A receptor, as do many exogenous hallucinogens such as DOB and LSD. Notably, LSD does not activate IP3 signalling through this receptor to any significant extent. This may explain why direct 5-HT2 agonists have psychedelic effects, whereas compounds that indirectly increase serotonin signalling at the 5-HT2 receptors, such as SSRIs, generally do not.
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