Nevertheless, Aricept remains the market leader in a highly profitable $3 billion a year business that is fore-casted to grow exponentially.

But there's one new drug that is beginning to challenge Aricept. It's called memantine (marketed as Ebixa, Axura, Namenda and Akatinol). Strictly speaking, it's not a drug, as it's derived from the naturally occurring mineral adamantine, and it also works in a different way from its pharmaceutical rivals. Developed by Merz, a German manufacturer of natural health products, the compound appears to protect brain cells against glutamate, the amino acid that is thought to be toxic to the brain in excess amounts and to trigger Alzheimer's.

Clinical trials of memantine have been promising, showing it to be particularly effective in moderate-to-severe AD, although it generally only slows mental decline rather than reverses it (Drugs, 2006; 66: 1515-34). Detailed testing has found that it appears to benefit attention and information-processing speed more than memory (Int J Geriatr Psychiatry, 2006; Nov 20; epub ahead of print).

Its side-effects are hardly greater than a placebo tablet, with a slight tendency to produce tiredness and dizziness. It is widely used in Germany, often in preference to the standard drugs; however, in Britain, it is still considered experimental.

Alternative treatments
Meanwhile, gradually emerging into the limelight are a number of promising plant-based treatments, some of which turn out to have properties that seem almost tailor-made for AD.

Take the humble culinary sage plant, Salvia officinalis. In addition to having potent antioxidant and anti-inflammatory effects, sage is known to have anticholinergic effects similar to Aricept's. When tested against placebo in a recent clinical trial, 60 drops of sage oil a day was often found to be better than Aricept at maintaining mental functioning in people with mild-to-moderate AD-and without any side-effects (J Clin Pharm Ther, 2003; 28: 53-9). Sage oil can also improve memory in younger people, too.

Lemon balm (Melissa officinalis) has been found to bind to the brain receptors believed to be involved with anxiety, thus reducing the agitation symptoms seen with AD. Particular strains of the plant have also proved able to slow the decline of mental functioning (Curr Pharm Des, 2006; 12: 4613-23). However, although some proponents recommend these plants as aromatherapy for Alzheimer sufferers, the evidence is considered "inconclusive" (Aust NZ J Psychiatry, 1999; 33: 789-99).

The classic herbal memory-enhancer is Ginkgo biloba, which has been proven in numerous clinical trials to benefit mental faculties in people of all ages. Germany is where it's most used for Alzheimer's, as even German conventional doctors consider it prefer-able to the pharmaceutical drugs on offer.

Although it's by no means a miracle-worker, Ginkgo has been shown to benefit virtually all AD patients to some degree, and about a third of them quite significantly. The recommended dosage is 240 mg/day of the Ginkgo extract codenamed 'EGb 761'; the benefits normally show up within six months (Pharmacopsychiatry, 2003; 36: 297-303). It's even been suggested that Ginkgo might help prevent the onset of AD but, so far, no research has been done to test its possible role in Alzheimer's prevention.

What of the other 'smart drugs' that are sometimes claimed to be memory-enhancers for the able-bodied? Of these, only nicergoline (derived from ergot) appears to have any evidence of benefit, with up to a threefold improvement on some performance measures in AD (Cochrane Database Syst Rev, 2001; 4: CD003159). Vinpocetine and piracetam, although better known, don't appear to have been adequately tested in Alzheimer's patients to come to any firm conclusions.