Chlormethine (INN, BAN), also known as mechlorethamine (USAN, USP), mustine, HN2, and (in post-Soviet states) embikhin (эмбихин), is a nitrogen mustard sold under the brand name Mustargen among others.

There have been studies demonstrating that topical administration of mechlorethamine has efficacy in mycosis fungoides-type cutaneous T cell lymphoma.

[15] When used in chemical warfare, it can cause immunosuppression and damage to mucous membranes of the eyes, skin, and respiratory tract.

Eye exposure causes lacrimation (tear production), burning, irritation, itching, a feeling of grittiness or dryness, blepharospasm (spasms of the eyelid), and miosis (pinpoint pupils).

Early symptoms include rhinorrhea (runny nose), epistaxis (nosebleed), toneless voice, sneezing, barking cough, and dyspnea (in smokers and asthmatics).

In severe cases, there may be epithelial necrosis throughout the respiratory tract, causing pseudomembrane formation, which can obstruct the airway.

[6] Though ingestion is uncommon, if mechlorethamine is swallowed it causes severe chemical burns to the gastrointestinal tract and concomitant nausea, vomiting, diarrhea, abdominal pain, and hemorrhage.

[6] Long-term effects of acute or chronic chlormethine exposure are caused by damage to the immune system.

[16] In 1935 several lines of chemical and biological research yielded results that would be explored after the start of the Second World War.

[20] The Yale pharmacologists Louis Goodman and Alfred Gilman were the first to conduct a clinical trial, on 27 August 1942, using the agent HN3 (tris(2-chloroethyl)amine) on a patient known as J.D.