Intracellular receptors are receptors located inside the cell rather than on its cell membrane . Classic hormones that use intracellular receptors include thyroid and steroid hormones. Examples are the class of nuclear receptors located in the cell nucleus and cytoplasm and the IP 3 receptor located on the endoplasmic reticulum . The ligands that bind to them are usually intracellular second messengers like inositol trisphosphate (IP 3 ) and extracellular lipophilic hormones like steroid hormones . Some intracrine peptide hormones also have intracellular receptors.
A receptor which is capable of producing a biological response in the absence of a bound ligand is said to display "constitutive activity".  The constitutive activity of a receptor may be blocked by an inverse agonist . The anti-obesity drugs rimonabant and taranabant are inverse agonists at the cannabinoid CB1 receptor and though they produced significant weight loss, both were withdrawn owing to a high incidence of depression and anxiety, which are believed to relate to the inhibition of the constitutive activity of the cannabinoid receptor.