Then I figured that cocaine users who might face employer drug tests use this to make sure they have been off the drug long enough not to get fired. Or, if not already employed, to make sure they can get hired by a company that does a pre-employment drug test.
Or maybe women who are about to start a family and who know of the drug's impact use the test to find out if the drug is out of their system before they get pregnant.
Or maybe parents use it to check out their kids.
That appears to be how the whole idea got started, according to this story in the New York Times from November 17, 1998:
Ms. Cloud, still suspicious of her son, decided to do her own drug tests, sending him into the family bathroom in boxer shorts with instructions to come out with a cup full of urine that she could ship to a local laboratory for analysis.
That is how Ms. Cloud began a cottage industry: the home drug testing business. ...Last month, the Food and Drug Administration approved the latest of these kits, the QuickScreen at Home Drug Test made by Phamatech, a San Diego manufacturer of diagnostic tests. The company bills its product as the first to give parents a result at home. Phamatech says that when the kit hits drug stores in December, screening for marijuana, cocaine, LSD or heroin will be as simple as taking a home pregnancy test.Whatever the reason, it is a sad statement that there is sufficient demand for this product to make it profitable and to have it sold by New York City's largest drugstore chain.