Medical students say they fear they are not being taught enough about anatomy and how drugs work.
Medical degrees focus more on communication skills
The British Medical Association's medical students conference said degree courses had changed to focus more on communication skills.
Daniel Gibbons, deputy chairman of the committee, said while students needed those skills, there was concern they were missing out on basic science.
But he stressed patients were not in danger because of the change.
Although some medical schools, such as Bristol and Cambridge continue to teach traditional, science-based courses, many have moved to focus more on communication skills and problem-solving.
Courses continue to teach students what happens in the body, and what drugs to give patients with particular conditions - but they say less about why this happens.
Students at the BMA conference were concerned that future doctors may not have the necessary background to deal with complex prescribing issues.
Mr Gibbons said: "Communication skills are obviously an essential for us. As doctors, we have to know how to communicate with patients in an open way.
"But the concern is that basic science doesn't get the priority it once did.
"We know what medicine to give for a particular illness.
"But we aren't taught how they actually work.
"Knowing that often helps communication by enabling us to explain to patients why a particular illness is progressing as it is."
But he stressed: "This change is not putting patients at risk."
Medical academics have also expressed concern that the move away from science based courses is reducing the number of graduates who want to work in clinical research - thereby reducing the pool of potential lecturers to teach the next generation.
Professor Michael Rees, chairman of the BMA's medical academic staff committee, said: "The balance has moved away in many, if not all, medical schools from the science-based curriculum.
"I think the problem is that its difficult to find the right balance."
He added fewer students were going into clinical research because of the change of focus at medical schools.
"It is very clear that academic medicine and science might have suffered."
And he said: "There's no hard evidence, but it could be that doctors trained in this way might be more susceptible to drug companies advertising.
"There is a concern that doctors won't be able to understand drug mechanisms and so wouldn't have the scientific knowledge to evaluate them."