The simple answer is that the medical board requires it. The full explanation is a bit longer and more involved. Let me see if I can elaborate without too much editorializing.
This all started with the 'opiate crisis". I put opiate crisis in quotation marks because whether or not there has been (the number of opiate related deaths seems to have peaked about 1-2 years ago) a crisis very much depends on where one lives. The story of America's opiate epidemic has been told in an excellent book, Dreamland: The True Tale of America's Opiate Epidemic by Sam Quinones. There are many individuals, corporate entities, and regulatory agencies that acted in their own self interest without regard for the longterm impact on patients and society at large. A short list of these entities include certain pharmaceutical companies, especially Perdue Pharma, an enterprising group of Mexican nationals, corrupt pill mills, the Joint Commission on the Accreditation of Hospitals, and the American citizenry's insatiable appetite for addictive psychoactive substances. Most of this is documented in the above referenced book.
Perdue Pharma developed and aggressively marketed the powerful narcotic Oxycontin. Oxycontin is about 1.5 times as potent as Morphine. Having a potent narcotic is welcome relief to those suffering for acute severe pain such as after surgery, major trauma or cancer pain. Compared to fentanyl, oxycontin is a lightweight in morphine equivalents. Fentanyl is 70 to 100 times as potent as morphine. Fentanyl is used multiple times each day in the operating and procedure rooms. If that were the end of the story all would be well.
Enter the Joint Commission on the Accreditation of Healthcare Organizations (JACHO). In the 1990's JACHO declared pain to be the 5th vital sign (after temperature, heart rate, blood pressure, and respiratory rate). This was not based on any scientific findings but was more of a compassionate public relations campaign foisted on the healthcare community. You will notice that the four standard vital signs are objectively measurable and reproducible both within the same patient and between patients. Pain, on the other hand is a totally subjective experience with a very strong emotional component. One might argue that psychiatrists deal with largely subjective symptoms and still manage to relieve suffering through the judicious use of medication. One difference is that for the major psychiatric disorders, excluding attention deficit disorder, the medication is largely non-addictive and not fatal in overdose. (Tricyclic antidepressants are the major exception to the fatality statement, and benzodiazepines to the addictive statement).
Oxycontin was supposed to have a coating that made it difficult or impossible to have it rapidly absorbed. Patients with addictions soon learned that this coating was easily removed and the oxycontin could be ingested or injected resulting in an immediate "high". To summarize: We have a potent opiate that can be injected for an immediate high, it is readily available not just for hospital use but for routine outpatient use, aggressively marketed to physicians and hospitals as a largely non-addictive or at least not likely to be abused pain reliever, a disorder, pain, which had previously been regarded as a symptom, the disorder is wholly subjective and not independently verifiable, and the leading accreditor of healthcare organizations (and if you don't have this accreditation you are out of business) telling the healthcare community they must aggressively treat pain as they would an elevated blood pressure or fever without regard to the underlying cause. What could possibly go wrong?
The rest of the story developed rapidly. Pill mills sprouted in Florida (why do scams of this sort seem to arise in Florida?) and West Virginia. Other areas had this pill mills but these areas were ground zero. The price of oxycontin on the street rose. A group of enterprising Mexican nationals saw a market niche and began importing tar heroin from Mexico. They had excellent customer service, prompt delivery, and they were able to undercut the price of oxycontin or white heroin from Asia. People began to die.
But I still don't understand why I have to take a UDS if I'm just taking Xanax 0.5 mg twice a day. The lethal dose of Xanax by itself is so large you would likely choke to death on the volume before you died from the drug. Also, if I'm a pain patient taking Percocet,
(a popular combination of oxycodone and acetaminophen) I would die from liver failure from the acetaminophen before dying from the oxycodone component. What gives?
Drug addicts don't use just one drug, they use drugs in combination. Among opiate addicts the favorite combination is an opiate with a benzodiazepine, most often Xanax or Klonopin. The opiate decreases respiratory drive and agitation associated with a decreased oxygen level and the benzodiazepine decreases arousal. The user is likely to die at lower blood levels of each drug when they are combined.
In 2016 the Centers for Disease Control (CDC) promulgated practice guidelines strongly recommending against the practice of combined prescriptions. About this same time, most states instituted the Prescription Monitoring Program (PMP), a computerized data bank of all controlled substances that is searchable by patient. Most states medical boards or legislatures have mandated the checking of the PMP and strongly recommend following the CDC guidelines. This approach is rational and will make the prescribing physician aware of any other controlled substance prescribed by another physician so that appropriate clinical decisions can be made with he patient.
As far as I can tell, through accessing data bases of drug laws in other states, Mississippi is the only state that requires a UDS for a routine benzodiazepine or other controlled substance prescription. If the physician follows the CDC guidelines and accesses the PMP before each benzodiazepine prescription, then the only patients that the UDS will "catch" are those that are taking opiates from friends, family or abusing heroin or buying opiates off the street. Experience with this screening will tell if this slice of the public is as large of a public health concern as the medical board has indicated.