A minimum price for alcohol in Wales could hit drinkers on low incomes and lead to some young people turning to drugs, a think-tank will tell AMs.
The Institute of Economic Affairs (IEA) will also claim it is "impossible" to predict how consumers will react.
The Welsh Assembly's health and social care committee is taking evidence on the proposed minimum 50p unit price.
It comes as updated research claims the policy will lead to 66 fewer deaths and 1,281 fewer hospital admissions a year.
Sheffield University's alcohol research group, which will also be giving evidence to AMs, was asked to update its modelling and original study.
It said on harmful drinkers:
- In the most deprived areas, they make up 0.6% of the drinker population
- But it is estimated they will experience 45% of the averted alcohol-attributable deaths and 24% of the averted alcohol-attributable hospital admissions
- They buy almost a half (46%) of their alcohol for less than 50p per unit
- They account for 4% of the drinker population, drink 27% of, and are responsible for 20% of all spending on, all alcohol consumed in Wales
- In contrast, moderate drinkers buy 22% of their alcohol for less than 50p per unit – so it is estimated the proposals will only cost them £8.30 extra per year
The committee is hearing different views on the proposed law, which was unveiled in October.
Under a 50p minimum unit price (MUP) formula, a typical can of cider would be at least £1 and a bottle of wine at least £4.69.
A typical litre of vodka, for example, would have to cost more than £20.
Pricing is seen as a "missing link" in public health efforts, alongside better awareness and treatment.
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Analysis by Owain Clarke, BBC Wales health correspondent
The latest study from Sheffield University, commissioned by the Welsh Government, once again suggests a minimum unit price of 50p for alcohol will have the greatest impact on hazardous and harmful drinkers.
But it is also true to say that the new law is likely to have more of a financial impact on less well-off drinkers.
Critics claim it is unfair that the poorest will once again be hit hardest – however worthy the aims of the law.
But due to the fact that very few places have introduced a minimum alcohol price, concrete evidence is scarce.
Much of the research is based on computer modelling and academic assumptions and predictions.
But until a minimum price is introduced, runs for a while and is subsequently analysed, it is impossible to say with certainty how and to what extent a minimum alcohol price will change behaviour and improve health.
The free market think-tank IEA, in its submission, said the only certain outcome is that it would raise the cost of a wide range of alcohol products.
"It will simply wipe out the bottom end of the market and force consumers who have a preference for budget brands to buy mid-range brands," said Chris Snowdon, the IEA's head of lifestyle economics.
"It is likely to lead to a shift from cider to spirits for dependent drinkers. A shift to the cheapest illegal drugs is also highly plausible among some groups, including young people."
He also claimed it could increase the cost of living for those who do not wish to drink less and is likely to lead to those on low incomes cutting other parts of the household budget, such as food and heating.
American economist Prof Jon P. Nelson is also sceptical about proposals, writing to the committee to say there was "virtually no support for the notion that MUP will be effective over the long-term in reducing heavy use of alcohol or alcohol-related harms".
But the Sheffield research group said MUP would target price increases on the cheaper and higher strength products which are disproportionately purchased by those at greatest risk of harm from their drinking.
"This means improvements in public health can be achieved while having only a small impact on moderate drinkers," said Dr John Holmes, senior research fellow, in his submission.
Health Secretary Vaughan Gething said the latest findings were further evidence of a "very clear and direct link" between excessive drinking and the availability of cheap alcohol.
He added: "All alcohol-attributable deaths are avoidable deaths – so by introducing this measure, we will save lives."
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