What a student misses by going alone, however, is the support provided by an academic adviser who will act as sounding board, guide and writer of the all-important letter of recommendation to medical school committees. Some programs have agreements with medical schools that offer qualified post-bac students early admission.

Columbia created the first post-bac program, in 1955, in its School of General Studies, intended for a postwar generation that was re-creating itself professionally.

Forty years ago, Southern Illinois University and Wayne State University in Detroit were pioneers in the profession’s efforts to recruit and train minority students who show promise in undergraduate pre-med curriculums but do not have the G.P.A. or MCAT scores to get them into medical school. Of the programs listed on the A.A.M.C. site, about 40 identify themselves as for “groups underrepresented in medicine.”

But in the past decade, it has been the older student looking for a second career in medicine that has driven the growth in the number and profile of the pre-med post-baccalaureates: about 80 programs are listed specifically for career-changers who lack science prerequisites; about 80 are labeled “academic record enhancers,” for recent graduates who took math and science but did poorly, or failed to get into med school the first time around. The programs are not interchangeable: programs intended to enhance grades assume a second pass at the material, and undergraduate and post-bac grades in those subjectsare usually melded to present to medical schools.

Students with none of the undergraduate courses that medical schools require should expect to take a minimum of two semesters each of chemistry, organic chemistry, biology and physics. (Post-bacs are typically full time and run 11 months to two years; some programs, like Drexel’s, offer evening classes; Northeastern University has an online option.)

Among the post-bac A.A.M.C. categories, career changers are the most academically successful, with matriculants earning an average MCAT score of 30.5 (out of 45); students in record-enhancer programs average 27.5. By contrast, the mean MCAT score for all pre-med matriculants is 31.1.

The laggard economy (what else?) is at least in part responsible for the post-bac boom. It is no coincidence, for example, that Columbia’s post-bac applications and ranks grew with former financiers and lawyers when the banking industry started its downward spiral. Or that many enterprising schools created programs (some better than others, experts warn) to tap into demand from the downsized looking for career fulfillment.Or that applications to medical school hit a record last year — almost 44,000 for less than half as many spots.