I think this was it, but I'm not sure. Google has decided it would rather be an adservice than a search engine.

https://www.ojp.gov/ncjrs/virtual-library/abstracts/why-drug-testing-bad-idea

The rest of the studies I have found say that drug-testing is simply ineffective and bad for morale.

Source ChatGPT Web Scan:

The claim about the Reagan administration conducting a study in the mid-1980s to demonstrate the effectiveness of workplace drug testing, and then trying to bury its negative results, is not supported by the available historical records.

The Reagan administration's drug policies in the 1980s, particularly under the Anti-Drug Abuse Acts of 1986 and 1988, focused primarily on increasing penalties for drug possession, creating minimum sentences for drug-related offenses, and addressing the crack cocaine epidemic. These policies were criticized for creating a racial and class imbalance in drug-related punishments and for being ineffective in addressing the systemic causes of drug abuse [❞] [❞] [❞] [❞].

Nancy Reagan's "Just Say No" campaign, which began in the early 1980s, aimed to spread awareness of the dangers of drug use, especially among youth. However, this campaign was criticized for oversimplifying the solution to drug abuse and for being largely ineffective in preventing adolescent drug use [❞].

There is no information available in the sources reviewed about a specific study on workplace drug testing being conducted and its results being suppressed by the Reagan administration, nor about Rolling Stone magazine suing the government for its release. The focus of the Reagan administration's drug policies seemed more oriented towards legislative measures and public awareness campaigns rather than workplace drug testing studies.