the σ1 receptor with a low affinity (Ki 2.6 μM). The consequences of this activity are unclear (as the role of sigma receptors in general is not yet that well understood). Due to this low affinity, therapeutic concentrations of memantine are most likely too low to have any sigmaergic effect as a typical therapeutic dose is 20 mg, however excessive doses of memantine taken for recreational purposes many times greater than prescribed doses may indeed activate this receptor. History Memantine was first synthesized and patented by Eli Lilly and Company in 1968 as an anti-diabetic agent, but it was ineffective at lowering blood sugar. Later it was discovered to have central nervous system (CNS) activity, and was developed by Merz for dementia in Germany; the NMDA activity was discovered after trials had already begun. Memantine was first marketed for dementia in Germany in 1989 under the name Axura. In the US, some CNS activities were discovered at Children's Hospital of Boston in 1990, and Children's licensed patents covering uses of memantine outside the field of ophthalmology to Neurobiological Technologies (NTI) in 1995. In 1998 NTI amended its agreement with Children's to allow Merz to take over development. In 2000, Merz partnered with Forest to develop the drug for Alzheimer's disease in the U.S. under the name Namenda. In 2000, Merz partnered with Suntory for the Japanese market and with Lundbeck for other markets including Europe; the drug was originally marketed by Lundbeck under the name Ebixa. Sales of the drug reached $1.8 billion for 2014. The cost of Namenda was $269 to $489 a month in 2012. In February 2014, as the July 2015 patent expiration for memantine neared, Actavis, which had acquired Forest, announced that it was launching an extended release (XR) form of memantine that could be taken once a day instead of twice a day as needed with the then-current "immediate release" (IR) version, and that it intended to stop selling the IR version in August 2014 and withdraw the marketing authorization. This is a tactic to thwart generic competition called "product hopping". However the supply of the XR version ran short, so Actavis extended the deadline until the fall. In September 2014 the attorney general of New York, Eric Schneiderman, filed a lawsuit to compel Actavis to keep selling the IR version on the basis of antitrust law. In December 2014, a judge granted New York