GP leaders say there is a crisis of confidence about a new NHS data-sharing scheme involving medical records.
From April, a giant database, Care.data, will be rolled out in England with non-identifiable records to help aid medical research and the monitoring of performance.
But the Royal College of GPs accused NHS England of failing to make the case for the project.
NHS England has said concerns about privacy are misplaced.
The warning comes after patient watchdog Healthwatch England said last week that the scheme should be delayed, as patients had been left "in the dark".
The central database will enable experts to assess diseases, examine new drugs on the market and identify infection outbreaks, as well as monitor the care patients get.
Information is already available about what happens in hospitals, but it has been difficult to link those records with information on what happens to patients when they are under the care of GPs.
However, concerns have been raised about the prospect of keeping all the information in one place, with campaigners saying that it could lead to privacy problems and data breaches.
There is a proposal - to be discussed next month - that could give access to non-NHS bodies, including private firms.
Meanwhile, NHS England has started a mass mailout to every household explaining the project and giving people the chance to opt out.
But Prof Nigel Mathers from the Royal College of GPs said the communications strategy had been inadequate.
"We are very concerned that, with just seven weeks to go before the national rollout, the public have not been properly informed about the benefits of, and the safeguards surrounding, the Care.data programme.
"The inevitable result of the failure to make the case for the scheme is the crisis of public confidence that we are now seeing.
"We urgently need a renewed national push by the authorities to ensure that patients are fully informed, in clear terms, about the benefits of the scheme, what their rights are, and what their rights to opt out are.
"Many GPs remain uncertain about the safeguards that will apply."
He said the college still remained "supportive" of the initiative in principle, but the government and NHS England needed to act immediately to restore public confidence.
A spokeswoman for NHS England said: "We're absolutely committed to ensuring the public are aware of the benefits of this initiative and their rights to opt-out.
"This is why we have sent a leaflet to every household in England. We have also provided leaflets and posters to every GP practice, articles in all the major newspapers, information on the NHS Choices website, information via social media, a video animation as well as information cascaded via 350,000 patient groups and charities."