Health: What's going on? I've got a friend with kidney failure who decided he didn't want a transplant ...

When I was training to be a GP, I changed a patient's tablets to a better brand. Well, they were cheaper. But it was the same generic drug, and the tablets were the same colour and shape. He came back a few days later. "Doctor, those tablets you gave me weren't the same." "What do you mean?" "Well, the first lot sank when I threw them down the toilet, and these ones floated."

It came as quite a shock at the time. But I consoled myself that he was a rare eccentric, and that the vast majority of my flock followed the doctor's orders. In fact, for chronic illnesses, the best estimate is that only half of all patients take their medicines in sufficient doses for them to be therapeutically effective - even for potentially life- threatening diabetes, epilepsy, asthma, leukaemia and high blood pressure. Indeed, according to one study, failure to take immunosuppressive medication is the commonest cause of kidney transplant failure. The costs of "non- compliance" in unnecessary disease, premature death and a waste of scarce health resources is staggering.

So what's going on? I've got a friend with kidney failure who decided not to go on the waiting-list for a transplant. "I looked into the side- effects of the drugs I'd have to take and decided it wasn't for me. Basically, the immune system of the rest of your body is completely clobbered to stop this foreign kidney being rejected. You feel like shit and you pick up every bug going. I see people on dialysis whose kidney transplants have failed, and I'm sure no one explained to them how horrible the drugs would be. It doesn't surprise me they don't take them."

Mark prefers to have dialysis, but even then he won't accept the whole package. "I'm supposed to have it three times a week, but sometimes I'll just do it twice. Other patients are on 12 different types of drugs to keep them going - they come in with bloody great carrier bags full of the things, and they look like death. Then the staff do blood tests and say things like: "Oh, your phosphate's really good", as if that's supposed to make up for it. They're so obsessed with their blood tests, they can't see the whole patient.

Mark takes only one of the many drugs he's been prescribed ("erythropoetin - the expensive one. I tried without it and my haemoglobin went down to seven) and he lets the staff take blood off him only once every three months. He ignores much of his strict diet and often trebles his daily 750ml fluid allowance. "Try limiting yourself to that. It's purgatory." He says he looks and feels better than anyone else in the unit. "You'd think the doctors would be interested in how I manage it, but they just get anxious and bolshie if you don't do it their way. When I first had dialysis, the nurse tried to add heparin to the blood to thin it. But I'd read that if you have heparin over a long period it increases your risk of osteoporosis. So I refused it. She got in a flap about how my blood would clog up the machine, so I had to be very firm with her. And did my blood clot? That's because I eat a healthy diet, drink what I want and don't stuff myself with their drugs."

A few years ago, non-compliance meant that you couldn't open the child- proof container (or couldn't find a child to do it for you), you couldn't afford to pick up the prescription, you couldn't remember to take it four times a day on a full stomach but avoiding dairy products or you found the side-effects so unpleasant that you returned apologetically to the doctor as if it was somehow your fault. True, there were always some patients who couldn't be arsed to do what they were told, but usually they wouldn't bother going to the doctor in the first place.

Mark, however, represents a new breed of patient willing to gather information about his treatment options and challenge the established wisdom of medicine from a position of strength. His arguments are part science, part belief and part bloody-mindedness, but it's sad that so many doctors should find this approach irritating and threatening. Why should you do what we tell you? "Doctor knows best" doesn't work any more. "Doctor and patient listen to each other, acknowledge each other's beliefs and feelings, negotiate a plan of action and monitor it together" isn't so catchy, but it's the only way forward.