if the dr is checking you its because of 2 reasons.
1- they want to make sure your not a drug addict and abusing other drugs also
2- they want to make are your levels are where they are supposed to be for your dose. they want to make sure that you are not selling it or taking it all in a week like an addict.
they are not gonna spend extra money for test for gear if they dont have to. they also just want to make sure that you are not gonna overdose by mixing other narcotics with what they are giving you. most drs dont care if u juice, they will actually help you and check your labs to make sure what you are doing is not too much to cause adverse reactions and sides.
i was on more pain meds than a dying cancer patient for 3 yrs for my back. they just want to make sure you are not gonna od from mixing stuff like opiates with benzos or adderals and shit. just checking your following the protocall on what they gave you and ur not an addict. but be sure that if they give it to you and u dont take them all then keep them in case they do a bottle count to make sure the extra pills are not being sold