Allopregnanolone is a naturally occurring neurosteroid which is made in the body from the hormone progesterone. As a medication, allopregnanolone is referred to as brexanolone, sold under the brand name Zulresso, and used to treat postpartum depression. It is used by injection into a vein over a 60-hour period under medical supervision.Side effects of brexanolone may include sedation, sleepiness, dry mouth, hot flashes, and loss of consciousness. It is a neurosteroid and acts as a positive allosteric modulator of the GABAA receptor, the major biological target of the inhibitory neurotransmitter γ-aminobutyric acid (GABA).Brexanolone was approved for medical use in the United States in 2019. The U.S. Food and Drug Administration (FDA) considers it to be a first-in-class medication. The long administration time, as well as the cost for a one-time treatment, have raised concerns about accessibility for many women. Medical uses
Brexanolone is used to treat postpartum depression in adult women. Side effects
Side effects of brexanolone include sedation (13–21%), dry mouth (3–11%), loss of consciousness (3–5%), and flushing (2–5%). It can also produce euphoria to a degree similar to that of alprazolam (3–13% at infusion doses of 90–270 μg over a one-hour period). Biological function
Allopregnanolone possesses a wide variety of effects, including, in no particular order, antidepressant, anxiolytic, stress-reducing, rewarding, prosocial, antiaggressive, prosexual, sedative, pro-sleep, cognitive, memory-impairment, analgesic, anesthetic, anticonvulsant, neuroprotective, and neurogenic effects.
Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula [CH3Hg]+. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a bioaccumulative environmental toxicant. Structure and chemistry
"Methylmercury" is a shorthand for the hypothetical "methylmercury cation", sometimes written "methylmercury(1+) cation" or "methylmercury(II) cation". This functional group is composed of a methyl group bonded to an atom of  mercury. Its chemical formula is CH3Hg+ (sometimes written as MeHg+). Methylmercury exists as a substituent in many complexes of the type [MeHgL]+ (L = Lewis base) and MeHgX (X = anion).As a positively charged ion it readily combines with anions such as chloride (Cl−), hydroxide (OH−) and nitrate (NO−3). It has particular affinity for sulfur-containing anions, particularly thiols (RS−). Thiols are generated when the amino acid cysteine and the peptide glutathione form strong complexes with methylmercury:
[MeHg]+ + RSH  →   MeHg−SR + H+

Sources
Environmental sources
Methylmercury is formed from inorganic mercury by the action of microbes that live in aquatic systems including lakes, rivers, wetlands, sediments, soils and the open ocean. This methylmercury production has been primarily attributed to anaerobic bacteria in the sediment. Significant concentrations of methylmercury in ocean water columns are strongly associated with nutrients and organic matter remineralization, which indicate that remineralization may contribute to methylmercury production. Direct measurements of methylmercury production using stable mercury isotopes have also been observed in marine waters, but the microbes involved are still unknown.