Clemastine, also known as meclastin, is a first-generation H1 histamine antagonist (antihistamine) with anticholinergic properties (drying) and sedative side effects.

[4] Clemastine is used to relieve hay fever and allergy symptoms, including sneezing; runny nose; and red, itchy, tearing eyes.

Stimulation is most common in children, and is usually followed by excitement, hallucinations, ataxia, loss of coordination, muscle twitching, athetosis, hyperthermia, cyanosis, convulsions, tremors, and hyperreflexia.

[6] Continuous and/or cumulative use of anticholinergic medications, including first-generation antihistamines, is associated with higher risk of cognitive decline and dementia in older people.

[12] Clemastine has been studied for its potential to treat several psychiatric and neurological disorders, including possibly promoting remyelination and myelin repair in conditions like multiple sclerosis (MS).

[15][16] However, a clinical trial (TRAP-MS) was halted in early 2024 after researchers found the disability progression was occurring at a significantly faster rate than anticipated in three participants with MS receiving clemastine.