However, multiple other NMDA receptor antagonists, including memantine, lanicemine, rislenemdaz, rapastinel, and 4-chlorokynurenine, thus far have failed to demonstrate sufficient effectiveness for depression. Furthermore, animal research indicates that arketamine, the enantiomer with a weaker NMDA receptor antagonism, as well as (2R,6R)-hydroxynorketamine, the metabolite with negligible affinity for the NMDA receptor, but a  potent alpha-7 nicotinic receptor antagonist may have antidepressive action. It is now argued that NMDA receptor antagonism may not be primarily responsible for the antidepressant effects of ketamine. Molecular targets
Ketamine principally acts as an antagonist of the NMDA receptor, an ionotropic glutamate receptor. The S(+) and R(–) stereoisomers of ketamine bind to the dizocilpine site of the NMDA receptor with different affinities, the former showing approximately 3- to 4- fold greater affinity for the receptor than the latter. As a result, the S isomer is a more potent anesthetic and analgesic than its R counterpart.Ketamine may interact with and inhibit the NMDAR via another allosteric site on the receptor.With a couple of exceptions ketamine actions at other receptors are far weaker than ketamines antagonism of the NMDA receptor (see the activity table to the right).Although ketamine is a very weak ligand of the monoamine transporters (Ki > 60 μM), it has been suggested that it may interact with allosteric sites on the monoamine transporters to produce monoamine reuptake inhibition. However, no functional inhibition (IC50) of the human monoamine transporters has been observed with ketamine or its metabolites at concentrations of up to 10,000 nM.
Desogestrel/ethinylestradiol (EE/DSG), sold under the brand name Marvelon among others, is a fixed-dose combination of desogestrel (DSG), a progestin, and ethinylestradiol (EE), an estrogen, which is used as a birth control pill to prevent pregnancy in women. It is taken by mouth.It was approved for medical use in the United Kingdom in 1981, and in the United States in 1992. In 2019, it was the 128th most commonly prescribed medication in the United States, with more than 5 million prescriptions. See also
List of combined sex-hormonal preparations § Estrogens and progestogens


== References ==