Beginning Thursday, doctors in New York who need to prescribe drugs to injured workers will be required to adhere to the state’s drug formulary, a new system that classifies drugs as appropriate or requiring preauthorization, and includes an online portal to preauthorize certain medications such as opioids.

Thursday’s launch — for new prescriptions only — is also the deadline for workers compensation payers to notify providers that injured workers on regular prescriptions of nonpreferred drugs such as opioids that they have seven months — until July 5, 2020 — to either wean the patient off the drug or go through the multistep preauthorization review process.

The drug formulary, which was approved by the New York State Workers’ Compensation Board in July and passed the legislature in 2017, aims to control prescribing of addictive, inappropriate or ineffective medications in the comp system, state regulators have said.

It is based on a “medication’s effectiveness and appropriateness for the treatment of illnesses and injuries covered under the Workers’ Compensation Law,” a board spokesperson wrote in an email Tuesday.

Similar to California’s drug list for injured workers, the New York formulary matches ailments with drugs the state found to be in line with medical treatment guidelines. However, unlike that of California, which lists specific ailments, the New York formulary lists body parts such as neck, knee or back and matches the body part to the drug that would be effective and in compliance — a method that might prove confusing, according to experts.

“I think there is potential for gray areas or confusion,” said Paul Peak, Memphis, Tennessee-based assistant vice president of clinical pharmacy for Sedgwick Claims Management Services Inc.

According to Mr. Peak, some of the confusion stems from the formulary’s rules on special considerations, such as when there is no body part listed on the formulary for which the doctor may be attempting to prescribe medication. The formulary lists eight body parts and four conditions, such as asthma or “pain non acute.”

Joe Paduda, president of Skaneateles, New York-based CompPharma LLC, said the formulary’s reliance on body parts could be problematic because a “knee” injury could mean many ailments — a nuance he called “nonsensical.”

“Based on a knee? You could have a torn (anterior cruciate ligament), arthritis or bad poison ivy,” he said. “What if it’s a broken kneecap or worn cartilage or an acid burn?”

Compliance may be another issue. Similar to California’s nearly 2-year-old formulary, which the state has grappled with getting doctors to comply with, the New York formulary does not include enforcement measures. Yet unlike California, which at first charged physicians to access the formulary, New York is granting free access to the drug list and treatment schedule, along with free access to the portal.

“I think a key problem with workers comp formularies that gets exacerbated by complexity is most providers rarely see workers compensation patients,” said Mr. Paduda. “How will they know how to comply? The more complex it is, the more problematic it is.”

“There will be no way to know who is using the portal; there is not a method to force the provider to use the portal,” said Mr. Peak.

While opioids are OK to prescribe on a first fill for up to seven days in a low dose, subsequent opioid prescriptions — common in workers compensation — will be subject to a preauthorization process, which will require that doctors submit documentation on why the drug is necessary.

In a webinar in November, Kimberly Di Scala, a Tucson, Arizona-based pharmacy program manager for First Script, Coventry Workers Comp, anticipates that lack of documentation from the provider will likely be the top reason for denials of drugs that require preauthorization.

The formulary also include two levels of appeals, with strict deadlines as to when doctors can appeal and when they can expect an answer — with the exception of the final appeal, for which there is no limit for how long the state’s medical board can take to approve or deny a drug, Ms. Di Scala noted in her presentation, adding that its likely to be the same as the previous appeal deadline: four days.

Another concern is that the formulary’s process could delay care.

“The regulators will say that this is the optimal way to handle a claim, which I don’t necessarily agree with. I don’t think they are considering how this thing works in the real world and how it works in the moment of care,” he said.

Concerns aside “we know those things are going to work themselves out,” said Mr. Peak, adding that the new formulary will likely result in doctors prescribing the more appropriate medications that are listed on the formulary.