Medical students are altruistic types willing to sacrifice their bodies in the pursuit of pharmaceutical excellence. But only if they're paid for it

"Have you still got the scars?"

"Yes."

"I bet mine are bigger."

"Tenner says they're not."

"Look at that then. Five at pounds 200 a line."

"Six at two-fifty each."

"OK you win. What other drugs did you do?"

A word of explanation for those of you who haven't been to a medical school reunion. We're talking Phase I pharmaceutical trials here. New drugs are invented by molecular roulette and then tried out on isolated animal tissues (eg intestines), whole small animals (eg rodents) and then whole larger animals (eg dogs)*. If all goes to plan, they're used on small numbers of human volunteers (eg medical students) to see how the body handles them and what, if any, side-effects occur.

Medical students, as you can imagine, are altruistic types willing to sacrifice their bodies in the pursuit of pharmaceutical excellence. But only if they're paid for it. In my time at St Thomas', I did just enough trials to keep a rosy glow on the cheeks of my bank manager, Mr Chipchase. We weren't allowed to be experimented on in our own hospital - that would have verged on the unethical - but the trials unit was only 15 minutes east by bicycle. Indeed, my happiest memory of medical school is cycling down the Waterloo Road with a 24-hour urine collection balanced on the handlebars.

I never did anything that physically scarred me, though these trials were ironically the safest; new batches of an established blood-thinning drug, which had to be test-run to check the bleeding time. Triallists were left with rows of small horizontal scars on their forearms, still evident 10 years on but far too neat to be confused with deliberate self- harm.

More risky was to try out a completely new type of drug. If you were lucky, you'd get the placebo (although you never knew if you had); otherwise, it was the real thing. To be fair, the risks were small - the trial dose was about a hundredth of the highest dose that the most sensitive lab animal could tolerate without side-effects - and it was certainly safer than dropping something unidentifiable in a night-club corner.

But side-effects did occur. In one trial, volunteers were given injections of an antibiotic into a muscle or a vein. A week later, they received the reverse. Those who had muscle before vein were, for complex immunological reasons, more likely to become sensitised to the drug and suffer an allergy to the intravenous injection.

The first in the queue had an anaphylactic reaction, not immediately life-threatening but enough to require emergency treatment. The second came over all queer and passed out. Incredibly, the rest of the volunteers in the queue - a mixture of students and Antipodean back-packers - all decided to continue with the trial, have the injection and take the money. pounds 500 was a lot in those days.

My memories of trials are not the side-effects but the boredom interspersed with hysterical laughter. One student tried to pass off a sample of tap water as his own urine to avoid failing the illicit drugs screen. He was called in to explain the high chalk content. Another, unable to cope with a lack of alcohol enforced on us during a five-day lock-in, escaped from the unit to the pub over the road. The unit's director arrived just in time to see him mooning at the rest of us from the saloon bar, a pint of lager in each hand. He was fined pounds 200, a lot to him but a trivial amount compared to what a drug company might lose if their new wonder-drug did unexpected things to the liver.

Nearly all of these trials were jobs for the boys. Female students, although equally poor, were generally excluded because of the risk that they might be pregnant. They could still experiment on each other in physiology practicals (passing tubes down each other's noses into the stomach, rebreathing from paper bags until you faint) but these tasks were to help us to be better doctors, not to pay off student loans.

I left medical school with a pounds 2,000 overdraft, but it would have been well over pounds 5,000 if I hadn't given my body to science. There were plenty of students who chose to stay deeply in debt rather than take the risk, but we all turned out much the same at the 10-year reunion (fat, bald, cynical, in debt). However, those who'd done the drug trials had one clear advantage. They had something to talk about ...

For those who dislike animal experimentation, it is worth pointing out that it has contributed to virtually every medical advance and useful drug, with the exception of digoxin and aspirin.