The introduction of 24-hour drinking laws may have trebled alcohol-related admissions to A&E departments in inner city areas at night, researchers say.
Few bars have asked to stay open for 24 hours
A study at London's St Thomas' Hospital compared overnight visits before and after the 2005 law change.
There were 80 alcohol-related visits in March 2005. This hit 250 in 2006, the Emergency Medicine Journal said.
Critics say data from one hospital cannot be applied to the whole of England and Wales.
However, the authors, who examined the emergency department at St Thomas' Hospital, said their study was representative of the problems in inner city areas across the country.
"If reproduced over longer time periods and across the UK as a whole, the additional numbers of patients presenting to emergency care could be very substantial," they said.
The figures, the authors suggest, "indicate that the legislation has had the opposite effect to that intended".
While those opposed to the November 2005 Licensing Act argued it would increase drink-related problems such as violence and illness, evidence up until now has either shown there has been little change or some reduction.
In November 2006 - one year on from the act - several NHS trusts reported that they had yet to see any adverse changes.
Two other studies, meanwhile, suggested that in some areas the level of violence had decreased - leading in turn to a fall in people arriving at A&E with alcohol-related assault injuries.
However, these studies did not take into account those arriving with health problems or self-inflicted injuries apparently caused by excess drinking.
Taking all these together, researchers at St Thomas' Hospital found that alcohol-related admissions trebled over that year.
The percentage change was slightly less dramatic, up from 3% of total visits in 2005 to 8% in 2006.
The researchers accepted that one of the reasons for the increase could be increased awareness among A&E doctors about alcohol-related problems.
This followed the intense media coverage of the introduction of the Licensing Act and its potential implications, they added.
But they said doctors had received no extra training, nor were they aware that a study was taking place.
Both the Department of Health and the Department of Culture, Media and Sport, which was behind the legislation, were dismissive of the findings, noting that the study only related to one hospital in one particular month.
The British Beer and Pub Association, meanwhile, stressed that alcohol sales across the country fell in 2006, and that the volume sold specifically through pubs and bars fell by more than 2%.
Many pubs have not applied for late licenses and those which have done so successfully are only staying open for an extra hour or so.
A spokesman for Alcohol Concern said: "It was always unlikely that a change in opening hours alone was going to move us to a continental style of drinking.
"Cheaper, non-alcoholic options, more food options, and 'cool off' zones within their establishments would all go a long way to minimising the risk of harm to revellers."