system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are pain management doctors required to obtain periodic drug screens but medical insurance companies not required to pay for those drug screens?

Several friends and patients are required to submit to periodic urine drug screens in order to remain in the care of their doctor but the insurance plan rarely pays for that required medical lab test.  Why?
gpt
Liability. 

The drug tests are to prove that the patient is actually taking the prescribed drug and not selling it, especially if it's a narcotic. If the patient is accused of selling their prescription narcotics, and the doctor has blood test results that support that accusation, the doctor can be charged with a crime. In addition, if the insurance company is found to have aided in the purchase of these narcotics (through medical coverage), they could be found liable, and assessed a fine by the federal government.

As for why the drug test isn't covered by the insurance company? That depends on what the test is submitted as. If the doctor's office submits the claim as "Insurer Mandated Drug Test", the insurer is probably going to reject that claim. If it is submitted as a generic "Blood Test", it has a better chance of being accepted as a valid claim.