In nearly all areas of medicine, the advances come so thick and fast that it can be hard to keep up with them. But, in one small corner of the medical world, things are still very much as they were in the 1930s. For the last 70 years, people with type I, or insulin dependent, diabetes (IDDM) have depended on daily injections of insulin to live.

Before the advent of insulin, many died painfully and prematurely. So, over the years, just keeping individuals with this crippling disease alive has been hailed a triumph, and rightly so.

But insulin is not a cure for diabetes, and its use has many downsides, including severe hypoglycaemia, which can result in coma. Even with insulin, many sufferers find that the complications of diabetes, which include nerve damage plus heart, eye and kidney disease, are overwhelming (Diabetes, 1999; 48: 2107-21).

Instead of looking for alternatives to insulin, drug companies have focused their minds and money on different ways of using insulin for example, as intermittent injections, in continuous insulin pumps or as an inhaled drug or on different types of insulin rapid acting, long acting and combinations of the two. The most devastating changes in insulin are the result of the development of alternative forms of insulin. For most of the 20th century, IDDM patients have used animal insulin, usually naturally derived from pigs or cows. Many did well on this, leading highly regimented, but otherwise normal, lives. Fifteen years ago, drug manufacturers began synthesising a new type of insulin, based on human proteins.

Scientists hailed the new insulin as a breakthrough. Despite being synthesised in the lab, they insisted that the new synthetic 'human' insulin was nearly identical to the natural animal variety. In fact, it is different from the animal variety in only one out of 51 amino acid residues. But the breakthrough was more of an aesthetic triumph than a medical one. Almost as soon as it was on the market, people who made the switch found that their health deteriorated.

The most worrying aspect of human insulin is that it appears to alter the diabetic's awareness of an oncoming hypoglycaemic episode, or 'hypo' (an extreme drop in blood sugar levels that can lead to unconsciousness and the need for medical intervention). By the early 1990s, patients were reporting personality changes, including increased feelings of aggression. In the UK, lawsuits were filed against the manufacturers of human insulin (MIMS, 1 August 1991: 12-3). The legal challenge failed, but patients continued to complain.

Between 1986 and 1989, the British Diabetic Association (BDA) whose mandate is to inform, advise and protect the interests of patients received some 3000 letters from people complaining about the adverse effects of human insulin. This prompted them to commission an independent report to analyse the content of those letters. The report was completed and due to be published in the British Medical Journal in 1993, but was suddenly withdrawn for being "too alarmist".

Six years after completion of the report, the document was leaked to the Guardian newspaper, which revealed its disturbing contents (9 March 1999).

The report gave often harrowing accounts of how people's lives had deteriorated after being switched to the synthetic insulin. Eighty per cent of the complainants examined said they could no longer control their symptoms and had lost the warning signs of an impending coma. From the data in the letters, the researchers concluded, among other things, that: