Selective androgen receptor modulators (SARMs) are a novel class of androgen receptor ligands. Selective estrogen receptor modulators, including raloxifene, tamoxifen and toremifene are banned. Benzodiazepines are positive allosteric modulators of the GABA type A receptors (GABA). This seems to be a common effect of many GABA receptor positive allosteric modulators. There are other Sphingosine-1-phosphate receptor modulators. SFRPs act as soluble modulators of Wnt signaling. Optical frequency combs generated with cascaded optical modulators also possess this property. First allosteric modulators were developed in 2018. Selective progesterone receptor modulators (SPRMs) are sometimes used to stop uterine bleeding. For example, O and CO are homotropic allosteric modulators of hemoglobin. Selective progesterone receptor modulators, such as progenta, have been under investigation. Another type of pharmacological selectivity that is unique to allosteric modulators is based on co-operativity. At least two types of positive allosteric modulators (PAMs) can be distinguished. As described previously, the molecules that underlie LTP can be classified as mediators or modulators. These devices have found applications in lasers, photodetectors, modulators, and switches for example.