One reason for limited savings in the first decade is that it would probably take a few years for copycat biologics to reach the market after the law was enacted. Another factor is that biologics accounted for only 16 percent  about $46 billion  of total prescription drug spending last year, according to the market researchers IMS Health. And pharmaceuticals represent only about 10 percent of the nation’s overall health care spending.

The real savings might come more than 10 years out, as new biologic drugs appeared and as biologics represented an increasingly greater part of overall spending on drugs. That ramp-up is already evident: Express Scripts, a pharmacy benefits manager, says its spending on biologics grew 10 percent last year, compared with 2.5 percent for other drugs.

But anyone expecting the price wars that ensue when generic pills come on the market  when prices often drop by more than 60 percent  might be disappointed by the way competition plays out in biologic drugs.

Because it is harder and costlier to make biologic drugs than it is to copy pills, fewer generic competitors are likely to enter the fray. Many experts, including the Federal Trade Commission, expect price declines of more like 10 to 40 percent in biologics.

Even that would be a substantial savings for the overall health care system. But for many individuals, a $35,000 copycat version of a $50,000 cancer drug would still be unaffordable.

Another factor is that generic biologics are likely to undergo greater regulatory scrutiny than generic pills require.

It is difficult or impossible to verify that a copy of a biologic is exactly the same as the original  which is why the drugs are often called “biosimilars” rather than generic biologics. Because even small changes might affect the drug’s safety or activity, it is likely that makers of biosimilars will have to conduct at least some clinical trials to win F.D.A. approval of their drugs, which makers of generic small-molecule pills are not required to do. Such trials can cost a lot of money.