Now here's a funny thing about prescription drugs. In the main they're taken by older people - in fact, one study revealed that, on average, a retired person may take at least three different drugs every day - and yet the drugs are rarely tested on elderly people before being licensed.

Usually pre-licensing trials recruit strapping young medical students who need to earn a few thousand extra quid (or dollars).

So when a drug is launched, nobody's too sure what effect it will have on its intended market.

Not surprisingly, perhaps, the elderly patient doesn't usually take to the drug quite as well as our young medical student. In fact, one study has discovered that up to 48 commonly prescribed drugs could pose 'unacceptable hazards' or simply be ineffective in elderly people.

Older people have slower metabolisms, chronic conditions and weak constitutions, and so drugs that they might have been able to tolerate even a few years previously now present a health hazard. New side-effects can also emerge as the patient ages.

So is the answer to include more elderly patients in pre-licensing trials? Theoretically, yes, but drug companies would never do that - because all the adverse reactions that would suddenly be reported would almost ensure the drug would never get its licence.

Silly of us for asking, really.

(Source: Washington Times, 15 December 2003, and British Medical Journal, 2004; 328: 176).