Mental health parity appeals often look straightforward on the surface: a plan denied residential treatment, intensive outpatient care, eating-disorder treatment, or substance use disorder care, and the claimant argues the denial was unfair. But many otherwise solid appeals lose force because they focus on the wrong issues, ask for the wrong records, or compare the wrong benefits.
That matters because federal parity law can be broader than many claimants realize. The Mental Health Parity and Addiction Equity Act, or MHPAEA, generally bars plans from applying financial requirements and treatment limitations to mental health and substance use disorder benefits in a more restrictive way than they apply comparable medical and surgical benefits. Federal agencies have continued to report widespread compliance problems, especially around nonquantitative treatment limitations, often called NQTLs—the behind-the-scenes rules that shape access to care through medical-necessity criteria, prior authorization, network design, reimbursement methods, and similar coverage controls. The Department of Labor’s 2025 Report to Congress describes corrections affecting more than 18 million participants during the reporting period, and notes that CMS continued to see zero comparative analyses that were sufficient on first submission. Federal regulators have also clarified that participants and their authorized representatives can request comparative information and other documents relevant to how an NQTL was applied.
In this post you’ll learn seven common parity mistakes that can weaken an appeal, what stronger framing may look like, and how an attorney may help turn a denial into a more evidence-based challenge. If you want a broader foundation first, it may help to start with this overview of how parity rules work in practice.
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One of the most common mistakes is arguing only that the treatment was “medically necessary,” without asking whether the standard used to judge medical necessity was itself applied unequally.
That distinction often changes the whole appeal.
Many denial letters focus on symptoms, progress notes, risk level, or discharge planning. Claimants then respond by sending more clinical evidence and arguing that the reviewer got the facts wrong. Sometimes that helps. But in parity cases, another question often matters just as much: Was the plan using a tougher rule for behavioral health care than it used for comparable medical or surgical care?
Federal guidance has repeatedly emphasized that plans must disclose the criteria for medical-necessity determinations for mental health and substance use disorder benefits, and must also disclose the reasons for denials. In ERISA-covered plans, claimants on appeal also have rights to documents relevant to the claim, including materials relied on, generated, or considered during the decision-making process. Those materials can include policies, guidelines, and information showing how the plan ensures consistent decision-making. DOL’s claims-procedure guidance lays out that disclosure framework, and the parity FAQs explain that these documents can include analyses of how an NQTL complies with MHPAEA.
Here’s what this often means in practice: a claimant may have a stronger argument if the appeal asks not only, “Was this treatment necessary?” but also, “What criteria did you use, where did they come from, and how do they compare with the criteria used for analogous medical/surgical care?”
That is often where stronger parity arguments begin.
Parity arguments rise or fall on comparison. If the comparison is off, the appeal can lose traction even when the denial feels deeply unfair.
For example, residential mental health treatment is often compared to some form of intermediate medical or surgical care, not necessarily to acute inpatient hospitalization. Courts and regulators have repeatedly wrestled with this issue, and recent decisions continue to show how important the comparator question is. In Ryan S. v. UnitedHealth Group, Inc., the Ninth Circuit reiterated that a parity claim turns on whether the plan imposed a more restrictive limitation on mental health treatment than on medical and surgical treatment, and the court allowed the plaintiff’s parity theory to move forward at the pleading stage. The opinion also reflects the broader reality that parity pleading can be difficult and fact-specific.
At the agency level, parity guidance has likewise stressed classification consistency. The 2024 final rule stated that comparable intermediate medical/surgical benefits and intermediate mental health/substance use disorder benefits must be assigned consistently across the existing classifications, although in May 2025 the Departments announced they were reconsidering parts of that 2024 rule and would not enforce the new provisions while litigation is pending and for an additional 18 months after a final decision. Even so, the agencies also stated that MHPAEA’s underlying statutory obligations, as amended by the Consolidated Appropriations Act of 2021, remain in effect. That enforcement statement is important because it means parity arguments did not disappear; the regulatory landscape just became more complicated.
A stronger appeal often identifies the closest analog: skilled nursing, inpatient rehabilitation, hospice, home health, or another medical/surgical service that functions at a similar level of care or under a similar utilization-management framework. If you are trying to spot these issues early, it may help to read more about how to recognize possible parity problems in a health plan’s rules and denials.
Some claimants assume parity only applies to obvious numerical restrictions like day caps, visit limits, or separate deductibles. Those issues matter, but modern parity disputes often center on NQTLs—rules that are not expressed numerically yet still control access to care.
Common NQTL examples include: