Tetrahydroaminoacridine (THA, tacrine), a cholinesterase inhibitor with several other actions that could enhance cognitive function,1 has passed the Food and Drug Administration's stringent licensing procedure for use in treating “mild to moderate” Alzheimer's disease.2

Since the first claim of its efficacy in Alzheimer's disease in a controlled trial in 19863 further studies have been almost equally divided between those reporting benefit for some patients with Alzheimer's disease and those reporting no benefit4 (such as the study by Maltby in this issue p 8795). No washout period or inadequate outcome measures are apparent in most studies, and comparison between them is also complicated by the concurrent use of lecithin in some studies. The dosage of tetrahydroaminoacridine varies widely, between 20 mg and 114 mg a day, as does the duration of treatment, from …