The public often defers to medical experts, but not always:

Imagine you are seated at a table with two bowls in front of you. One contains peanuts, the other tablets of the illegal recreational drug MDMA (ecstasy). A stranger joins you, and you have to decide whether to give them a peanut or a pill. Which is safest? You should give them ecstasy, of course. A much larger percentage of people suffer a fatal acute reaction to peanuts than to MDMA. … 

As New Scientist went to press, the UK government's Advisory Council on the Misuse of Drugs was widely expected to recommend downgrading it, based on evidence of its limited harmfulness (see "Ecstasy's legacy: so far, so good"). Yet the government has already rejected the advice.

No doubt this is partly a reaction to the furore over the government's de facto decriminalisation of cannabis in 2004, based on another advisory council recommendation. Despite the fact that the move actually reduced the quantity of cannabis being smoked … the government recently reversed it in the face of implacably bad press.

For evidence of how irrational and lacking in perspective the public debate has become, consider how the advisory council's chairman, David Nutt, found himself in hot water last weekend for comparing the harm caused by ecstasy to the harm caused by horse riding.

How does the public decide when to believe medical experts and when not to?