The classification of alpha and beta subtypes of the adrenergic receptor results from the diverse responses towards adrenergic stimulation. Epinephrine and norepinephrine are the primary adrenergic neurotransmitters. The receptors are part of the super family of metabotropic G-protein coupled receptors (GPCR-A17), and are often referred to as being responsible for the ‘flight or fight response’. Activation of the alpha subtype generally results in vasoconstriction, whereas activation of the beta subtype leads to vasodilatation. While beta blockers are generally known for their management of cardiac arrhythmias, cardioprotection after myocardial infarction (heart attack), angina and hypertension (e.g. Axon 1159 (Celiprolol hydrochloride), and Axon 1518 (Timolol maleate)), in contrast, drugs interacting at the alpha adrenergic receptors are often used for a variety of medical disorders; e.g. for the treatment of hemorrhagic shock (Axon 1154, B-HT 933 dihydrochloride), as an antidepressant, antidiabetic, or to prevent central neurodegenerative disorders (e.g. Axon 1155, Efaroxan hydrochloride), or for the treatment of narcolepsy and sleep disorders (e.g. Axon 1296, Modafinil).
(Nor-) Adrenergic receptor subtypes listed: Adrenoceptor α1, Adrenoceptor α2, Adrenoceptor β1, Adrenoceptor β2, Adrenoceptor β3
 G-Protein-coupled receptors: Better beta-blockers. J. Owens. Nature Reviews Drug Discovery 2005, 4, 371.
 Pressor effects of the alpha 2-adrenoceptor agonist B-HT 933 in anaesthetized and haemorrhagic rats: comparison with the haemodynamic effects of amidephrine. M. R. MacLean, M. Thomson, C. R. Hiley. Br J Pharmacol. 1989, 97, 419-432.
 Use of efaroxan and derivatives thereof for the treatment of Alzheimer's disease. F. Colpaert et al.US patent US4855385, 1989.
 Randomized trial of modafinil as a treatment for the excessive daytime somnolence in narcolepsy. Becker PM, et al. Neurology 2000, 54, 1166-1175.