A restricted class of OTC drugs also exists in the . This restricted class includes drugs such as pseudoephedrine, emergency contraception, and some Schedule V controlled substances. These products, while considered OTC, are kept behind the pharmacy counter and must be dispensed by a pharmacist pursuant to proper identification, age verification, and patient education. In March 2012, the FDA considered expanding the definition of nonprescription drugs to include cholesterol, blood pressure, asthma and birth control medications. This new Rx-to-OTC switch ruling is currently under review and commenting.
The OTC Markets Group operates some of the most well-known networks, such as the OTCQX Best Market, the OTCQB Venture Market and the Pink Open Market. These markets include unlisted stocks that are known to trade on the Over the Counter Bulletin Board (OTCBB) or on the pink sheets . Although Nasdaq operates as a dealer network, Nasdaq stocks are generally not classified as OTC because the Nasdaq is considered a stock exchange. Conversely, OTCBB stocks are often either penny stocks or are offered by companies with bad credit records.
In their 2000 paper by Schinasi et al. published by the International Monetary Fund in 2001, the authors observed that the increase in OTC derivatives transactions would have been impossible "without the dramatic advances in information and computer technologies" that occurred from 1980 to 2000.  During that time, major internationally active financial institutions significantly increased the share of their earnings from derivatives activities. These institutions manage portfolios of derivatives involving tens of thousands of positions and aggregate global turnover over $1 trillion. At that time prior to the financial crisis of 2008, the OTC market was an informal network of bilateral counterparty relationships and dynamic, time-varying credit exposures whose size and distribution tied to important asset markets. International financial institutions increasingly nurtured the ability to profit from OTC derivatives activities and financial markets participants benefitted from them. In 2000 the authors acknowledged that the growth in OTC transactions "in many ways made possible, the modernization of commercial and investment banking and the globalization of finance."  However, in September, an IMF team led by Mathieson and Schinasi cautioned that "episodes of turbulence" in the late 1990s "revealed the risks posed to market stability originated in features of OTC derivatives instruments and markets.