Patients who smoke, drink too much or are obese could be denied medical help if their lifestyle is likely to undermine their treatment, the government's health treatment watchdog said yesterday.

A report published by the National Institute for Health and Clinical Excellence (Nice) said: "If the self-inflicted cause of the condition will influence the likely outcome of a particular treatment, then it may be appropriate to take this into account in some circumstances."

But it warned doctors they must not discriminate against patients with conditions that are, or may be, self-inflicted.

Nice also said that the report - entitled Social Value Judgements: Principles for the Development of Nice Guidance - would not be issued as guidance in the NHS and that individual patient care would still be left up to doctors, nurses and other NHS health workers.

But its recommendations would be used in developing policy at Nice, which has proven influential in formulating rules for NHS treatments since it was set up six years ago. The report also pointed out the inherent difficulty in determining whether someone's illness was self-inflicted or not. It noted that there was no way of being sure whether a smoker who had a heart attack would have suffered one had they not smoked.

But while it advised against discriminating against people with problems that are, or could be, self-inflicted, it said: "A patient's individual circumstances may only be taken into account when there will be an impact on the clinical and cost effectiveness of the treatment."

The recommendations followed the news last month that obese people would not be entitled to hip and knee replacement surgery on the NHS in East Suffolk because of budget constraints. That ruling came as part of a series of measures to be taken by the three primary care trusts in the area in an attempt to save money locally for the NHS. It is believed that the risks of operating on obese patients are higher and the treatment may be less effective, with replacement joints wearing out sooner.

Nice said clinical guidance should only recommend a treatment for a particular age group where there was clear evidence of a difference in the treatment's effectiveness for that age group. It advised that drug treatment for flu should be available for people over-65 as they were more likely to be seriously affected than younger people and that IVF treatment should be available to women aged 23-39 because success rates in this group were higher than in other age ranges.

Steve Webb, the Liberal Democrats' health spokesman, said: "There is no excuse for cash-strapped hospitals denying treatment to people whose lifestyle they disapprove of. Treatment decisions involving people's lifestyle should be based on clinical reasons, not grounds of cost."

A spokeswoman for Nice defended the report, saying: "We want to reassure people that in producing our guidance we are not going to take into consideration whether or not a particular condition was or is self-inflicted. The only circumstances where that may be taken into account is where that treatment may be less effective because of lifestyle choices."