Health Check: Jeremy Laurance

What happened to all the old certainties?

When Franklin Roosevelt coined the phrase "We have nothing to fear but fear itself" – a soundbite that has echoed across the decades and acrossthe Atlantic in recent weeks – he did not say what he meant. Apt as it appears in the context of the terrorist threat under which we all now live since 11 September, it is not fear that we fear but uncertainty.

Uncertainty is the driver of most health scares. Flu kills 4,000 people in the UK in a good year, when the virus is a mild strain, and more than 20,000 in bad years when we get a nasty strain that triggers an epidemic. Do we see people out on the streets wearing gas masks in winter? I think not.

Flu is unlike anthrax in one critical respect. We are familiar with it. We know about the fever, the aches and pains and the irresistible desire to lie down that are its hallmarks. We dose ourselves with paracetamol and whisky and sweat it out, hoping for the best. We tend, perhaps, to turn a blind eye to its real, lethal effects.

We not only know little about anthrax, but that little is being revised day by day, hour by hour. Uncertainty, rather than diminishing, is growing. It is now apparent that the public health experts in the US did not realise how easy it was to disperse the spores in quantities sufficient to cause pulmonary anthrax – the most lethal sort – and that was why they initially discounted the risk to the postal workers who had handled contaminated envelopes on the basis that it would be lower than the risk for those who opened them. How wrong, we now know, they were.

It is difficult to live with uncertainty, but we are learning that we have to. Doctors and scientists don't have all the answers. Frequently, new information only extends our uncertainty. And this was true before 11 September.

Are mobile phones safe? There is no evidence that they cause harm – so far – but the jury is still out. On the precautionary principle, children, whose skulls are thinner and developing brains more vulnerable, are advised to minimise use. The rest of us continue to use them in a state of – blissful? – ignorance.

Is lamb safe? Here there is new uncertainty since a study designed to show whether BSE had spread into sheep ended in disaster with the discovery that the brains the researchers were studying actually came from cows. We may now never know whether BSE was transmitted to sheep.

Is having a baby by Caesarean safer than natural childbirth? A major study last week found the Caesarean rate had risen to an all-time high, accounting for more than one in five of all births. But the question every mother-to-be is asking is one that no one can answer. The Royal College of Obstetricians says it is still unclear about the balance of risks and is therefore not prepared to pass judgement on the high Caesarean rate.

What of cannabis? David Blunkett's proposal to re-classify it as a class C drug, making possession a non-arrestable offence, will undoubtedly reduce pressure on the police. But will it reduce the harm caused by the drug?

Here, it is possible to give an unequivocal answer: no. Throughout recorded history the damage caused by a drug has been closely linked to its availablility. Cut the price of alcohol and you end up with more alcoholics. Extend pub opening hours and you reduce the damage caused by binge drinking but you increase the quantity drunk.

The uncertainty here is of a different kind: whether the damage caused by increasing consumption – the greatest danger, I think, is cannabis's demotivating effect – will be outweighed by the benefit of freeing police to chase other, more serious, crimes. I suspect it will, which is why I support Blunkett's move. But it is a gamble, none the less, and the outcome – uncertain.