More specifically, what would have been the drug of choice used to treat a highly aggressive patient circa 1890? Was restraint the only available option?
Restraint would have been common until the late 1940's - early 1950's when medication became commonplace. One of the first psychiatric drugs (that's still used today) to treat mania is Lithium citrate which was rediscovered in 1948 by Australian psychiatrist, John Cade.