He said he had been turned down by a fast-food restaurant because of his marijuana conviction, as well as at the restaurant where he worked before his last arrest as a fry cook and dishwasher. “I’ve kind of stopped trying,” said Cory, who is African-American.

Tess Borden, a fellow at Human Rights Watch and the A.C.L.U., who wrote the report, found that despite the steep decline in crime rates over the last two decades — including a 36 percent drop in violent crime arrests from 1995 to 2015 — the number of arrests for all drug possessions, including marijuana, increased 13 percent.

The emphasis on making marijuana arrests is worrisome, Ms. Borden said.

“Most people don’t think drug possession is the No. 1 public safety concern, but that’s what we’re seeing,” she said.

Criminologists say that African-Americans are arrested more often than whites and others for drug possession in large part because of questionable police practices.

Police departments, for example, typically send large numbers of officers to neighborhoods that have high crime rates. A result is that any offense — including minor ones like loitering, jaywalking or smoking marijuana — can lead to an arrest, which in turn drives up arrest rate statistics, leading to even greater police vigilance.

“It is selective enforcement, and the example I like to use is that you have all sorts of drug use inside elite college dorms, but you don’t see the police busting through doors,” said Inimai M. Chettiar, director of the Justice Program at New York University’s Brennan Center for Justice.

African-Americans may also be more apt to face arrest, according to researchers, because they might be more likely to smoke marijuana outdoors, attracting the attention of the police.