The InDependent Diabetes Trust, which makes a fictionalised appearance in the novel (as the good guys), has an interesting article about this. The article advises not abdicating your own judgment by simply assuming that experts must be right, especially when those experts are driven by considerations other than your preferences. Dead Level follows the standard convention of fiction that when doctors turn bad it is due to financial motives, but there are other reasons why medical professionals can be dangerous to your health.
The diabetic community cannot survive without this life-saving drug. We therefore form a captive market and, as any economist will tell you, this creates a perfect opportunity for experts to manipulate and exploit us. Have our gurus the time or inclination to guide us through this jungle of short, medium, long-term and mixed insulins? Do they explain the scientific jargon and help us make a free and informed choice? [...]
Three clues will help us make up our mind. The first is not to abdicate in favour of the care team or encourage them to steal our melody. The second clue is not to make a decision until you have in front of you a complete list of all insulins on the market, both animal and 'human'. Thus fortified, you and your helpers can work out what is possible for you. An informed, rather than an imposed, choice will result. The third clue is not to believe what the printed instructions tell you about the strength and duration of action of each kind of insulin.
I prefer to use the term "preferences" in relation to patients. As I pointed out in The Power of Life or Death, the phrase "best interests" is often misused, for example when doctors or judges claim it is in a patient's best interests to die — even when the patient didn't express a wish to do so. The modern state-remunerated doctor may well be incentivised to keep his patients in the dark, and may indeed feel morally justified in doing so.