Urging people to have Dry January risks sending an "all or nothing" message and could do more harm than good, an expert has warned.
The no-booze campaign is run by Alcohol Concern, and figures suggest that last year more than two million people cut down their drinking for the month.
The campaign says there are "significant health benefits" from taking part, from "weight loss and better sleep ... to more money in your pocket".
But Ian Hamilton, a lecturer in the Department of Health Sciences at York University, said that just because Dry January is popular, it "does not mean it is effective".
Writing in the British Medical Journal (BMJ), he said: "Alcohol Concern's ambition is to alter people's relationship with alcohol by encouraging us to reduce the amount we drink, not just for a month but for life.
"Unfortunately, this type of campaign has had no rigorous evaluation."
Mr Hamilton said it was not clear who Dry January is targeting and those taking part may drink the least amounts anyway.
"Because participants select themselves, it could attract the people at lowest risk from health problems related to alcohol," he said.
"Because they consume less alcohol, they are also likely to find a month of abstinence relatively easy."
Mr Hamilton also said people tended to be "economical with the truth" when it comes to how much they drink.
He added: "Dry January risks sending out a binary, all or nothing, message about alcohol - that is, either participate by abstaining or carry on as you are."
He argued: "People may view their 31 days of abstinence as permission to return to hazardous levels of consumption till next New Year's Day.
"'I've had a month off, so now I can drink as much as I did before', ignoring the need for regular breaks from alcohol."
Among heavy drinkers, "abrupt abstention from alcohol" could also induce serious symptoms, such as seizures, he added.
"In sum, parched of evidence Dry January could have unintended consequences which would do more harm than good."
In an opposing view, Professor Sir Ian Gilmore, an honorary consultant physician at the Royal Liverpool University Hospital, who is on the board of trustees at Alcohol Concern, asked what was wrong with Dry January.
He wrote: "Our per capita consumption has doubled over 40 years, we have 1.5 million heavily-dependent drinkers in this country, and alcohol has become a central part of most social occasions.
"So what could possibly be wrong with encouraging and supporting the estimated two million or so adults who decide on Dry January to take a month off the booze and have time to reflect on their drinking?"
He said the campaign had been shown to have effects past the month of January.
Evaluation of the 2015 campaign by Public Health England showed that 67% of participants said they had had a sustained drop in their drinking six months on. Some 8% also "stayed dry".
Sir Ian added: "In an earlier evaluation by the University of Sussex, 79% of participants said they saved money, 62% of participants said they slept better and had more energy, and 49% said they lost weight."
Furthermore, people experienced "relief that they are not as dependent on that regular 'anxiolytic agent' as they thought; there is a life out there that does not have to revolve around drinking".
Sir Ian said Dry January should not be treated as a fundraising endeavour "culminating in drunken celebration at the month's end, nor as an excuse for thinking 'job done; body detoxed; I can go straight back to the old ways for the rest of the year'".
He also said heavy drinkers were advised to see their GP before stopping suddenly and completely.
The debate comes a week after the UK's chief medical officers issued new guidance saying no level of regular drinking is without risk to health.
Jackie Ballard, chief executive of Alcohol Concern, said the campaign was evaluated "to ensure that it really does work in the long term, not just for the month of January".
She said alcohol is linked to more than 60 medical conditions and recent research showed that having just one month off has "a positive impact on blood pressure, cholesterol and liver".