Cognex® (tacrine hydrochloride) is a reversible cholinesterase inhibitor, known chemically as 1,2,3,4-tetrahydro-9-acridinamine monohydrochloride monohydrate. Tacrine hydrochloride is commonly referred to in the clinical and pharmacological literature as THA. It has an empirical formula of C13H14N2•HCl•H2O and a molecular weight of 252.74. The molecular formula of tacrine hydrochloride is: Tacrine hydrochloride is a white solid and is freely soluble in distilled water, 0.1N hydrochloric acid, acetate buffer (pH 4.0), phosphate buffer (pH 7.0 to 7.4), methanol, dimethylsulfoxide (DMSO), ethanol, and propylene glycol. The compound is sparingly soluble in linoleic acid and PEG 400. Each capsule of Cognex® contains tacrine as the hydrochloride. Inactive ingredients are hydrous lactose, magnesium stearate, and microcrystalline cellulose. The hard gelatin capsules contain gelatin, NF; silicon dioxide, NF; sodium lauryl sulfate, NF; and the following dyes: 10 mg: D&C Yellow #10, FD&C Green #3, titanium dioxide; 20 mg: D&C Yellow #10, FD&C Blue #1, titanium dioxide; 30 mg: D&C Yellow #10, FD&C Blue #1, FD&C Red #40, titanium dioxide; 40 mg: D&C Yellow #10, FD&C Blue #1, FD&C Red #40, D&C Red #28, titanium dioxide. Each 10-, 20-, 30-, and 40-mg Cognex® (tacrine) capsule for oral administration contains 12.75, 25.50, 38.25, and 51.00 mg of tacrine HCl, respectively.