I'm not sure how you feel you have any control by using a drug test, Sunflower? Seriously, and I mean no disrespect.
Drug tests are degrading to the tested and the tester. They serve a good purpose for employment safety and some other good reasons, but home tests would reduce me to a place I don't want to be.
Tests can be faked, easily. They are good for the moment you take them and a half hour later mean nothing. Even under the best conditions they don't always work.
They use or they don't use...our instinct is the best drug test around. And all the drug tests in the world won't stop an addict from using.
Hugs