A survey of more than 1,000 medics found the majority believe the impact on the NHS of leaving the European Union will be negative.
It came as an online poll by Sky News found that half of UK voters would back a fresh three-option referendum on the final Brexit deal.
Last week a YouGov poll found that a majority of respondents backed a vote on the UK’s Brexit terms for the first time since the 2016 referendum.
Downing Street insisted the government is engaged in “good planning” and taking “sensible precautions” in case there is a no-deal Brexit.
Ministers have confirmed efforts to stockpile medicines and ensure an “adequate” food supply if there is a no-deal Brexit.
But Brexiteers have criticised the approach, insisting that, while preparations must be made to show Brussels that the UK could cope without a deal, the plans should not mark a return to the referendum campaign’s “Project Fear”.
Dozens of technical notices setting out what businesses and concerned citizens need to do are expected to be published in August and September.
The Prime Minister’s spokesman said plans are aimed at ensuring an “orderly” Brexit even if there is no agreement with Brussels.
But they played down reports that the military had been put on stand-by to deal with a no-deal scenario, saying there are “no plans to involve the army in this”.
In a study published in the Journal of Epidemiology and Community Health, three quarters of the 1,172 UK doctors surveyed via the online professional network doctors.net.uk said they voted to remain in the EU, and nearly all agreed that European NHS staff should be able to stay in the UK after Brexit.
Dr Kate Mandeville, lead author from the London School of Hygiene and Tropical Medicine, said: “This research comes at an important juncture in UK politics. Doctors are amongst the best-placed people to understand the impact of political decisions on the NHS.
“On Brexit their opinion is very clear: Brexit is bad for the nation’s health.”
Commenting on the study, Dr Andrew Dearden, treasurer at the British Medical Association, said: “The challenges posed by Brexit are considerable and though there has been some progress, there is too much uncertainty around what the implications will be for doctors and the health service.
“We already know, for example, that Brexit has already had a huge impact on the morale of EU NHS staff working here – our own research has shown us that almost half of NHS staff from the EU are considering leaving the UK because of the EU referendum.
“It is imperative that the public has a say in any proposed Brexit deal.”
According to the Sky News data poll, when asked to choose between three options – May’s deal, a no deal or staying in the EU – 48 per cent said they would prefer to stay in the EU, 27 per cent wanted to leave with no deal and 13 per cent would opt for the government’s deal.
Meanwhile, 78 per cent of the public think May’s government is doing a bad job on negotiating Brexit.
Sky Data interviewed a nationally representative sample of 1,466 Sky customers online between 20 and 23 July.