Although tacrine was marketed for many years as a respiratory stimulant, only recently has it been prescribed to treat the symptoms of mild to moderate Alzheimer's disease. Marketed under the trade name Cognex, the reversible cholinesterase inhibitor does not cure or slow the progression of the debilitating disease, but rather allows the patient to improve thinking ability.

Tacrine is known as 1,2,3,4-tetrahydro-9-acridinamine monochloride monohydrate (or tetrahydroaminoacridine) to biochemists and features 13 carbons, 14 hydrogens, 2 nitrogens plus a molecule of water (2 hydrogens and 1 oxygen) and a molecule of hydrochloric acid (1 hydrogen and 1 chlorine atom) for a molecular weight of 252.74. Tacrine hydrochloride (THA) forms a white solid that is readily water-soluble and soluble in organic solvents. The octahedral crystals of the hydrochloride formulation have a melting point of 283 to 284 degrees Celsius and a bitter taste.

Tacrine slows the breakdown of the chemical messenger acetylcholine, which is apparently accelerated in the cerebral cortices of early Alzheimer's sufferers. There are some indications that HIV/AIDS dementia patients may show significant increases in white blood cell counts and some improvements in movement disorders when taking tacrine. Unwanted side effects of drug therapy with Cognex includes nausea, blurred vision, confusion, shortness of breathe, weakness, and liver problems. Overdoses can cause low blood pressure, extreme weakness, and possible convulsions. In the Ames test, tacrine hydrochloride was mutagenic to bacteria, and as a member of the acridine chemical class, is probably a carcinogen.