People who signed up early for insurance through the new marketplaces were more likely to be prescribed drugs to treat pain, depression and H.I.V. and were less likely to need contraceptives, according to a new study that provides a much-anticipated look at the population that signed up for coverage under the new health care law.

The health of those who enrolled in new coverage is being closely watched because many observers have questioned whether the new marketplaces would attract a large share of sick people, which could lead to higher premiums and ultimately doom the new law.

The study, to be released Wednesday by the major pharmacy-benefits manager Express Scripts, suggests that early enrollees face more serious health problems and are older than those covered by their employers. The study also showed a higher use of specialty drugs, which are often used to treat diseases like cancer and rheumatoid arthritis; the use of such drugs could hint at more costly medical problems…

Still, she and others cautioned that it was too early to properly evaluate the health of those who were signing up. The study by Express Scripts looked at a sample of 650,000 consumers who received coverage in January and February and did not capture information about those who signed up closer to the enrollment deadline. Insurers have said anecdotally that those who signed up later tended to be younger and were presumably healthier.