Smokers, drinkers and overweight people may be refused treatment on the NHS. If patients' lifestyles will hinder their recovery or make treatment ineffective, doctors may deny them certain drugs or operations, the Government's treatment watchdog said today.

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 doctors should avoid discriminating against patients with conditions that are, or may be, self-inflicted, it said in a report issued yesterday.

Last month, East Suffolk NHS announced that obese people would no longer be given hip or knee replacements. GPs and consultants agreed not to refer anyone classed as obese to a specialist until they have lost weight, in order to to save the area's primary care trusts (PCTs) £47.9m.

Speaking at the time Dr Brian Keeble, the director of public health for Ipswich PCT, said: "Patients who are overweight and obese do worse after operations. Lighter people tend to do better in terms of hip replacements not failing. But we cannot pretendthis work wasn't stimulated by the pressing financial problems of the NHS in East Suffolk."

The report considered whether social background, age or lifestyle choices should ever influence the care provided by the NHS. It concluded that 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.

NICE has made judgements that take into account age, such as the recommendation that drug treatment for flu should be available for people over 65 who are considered vulnerable and IVF treatment should be available to women aged 23-39 because it is most likely to be effective in this group.

Professor Sir Michael Rawlins, the chairman of NICE, said: "On age we are very clear - our advisory groups should not make recommendations that depend on people's ages when they are considering the use of a particular treatment, unless there is clear evidence of a difference in its effectiveness for particular age groups. Even then, age should only be mentioned when it provides the only practical 'marker' of risk or benefit. NICE values people, equally, at all ages."

The report was criticised by the Liberal Democrats. Their health spokesman, Steve Webb, 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. The NHS is there to keep people healthy, not to sit in judgement on individual lifestyles."

Jonathan Ellis, the policy manager for the charity Help the Aged, said: "We're pleased to see Nice has finally shown an understanding of the importance of tackling age discrimination within health care."