Skrmetti: The Supreme Court reaffirms that biology matters

This is part of SCOTUSblog’s term in review series, in which scholars analyze some of the most significant cases of the 2024-25 Supreme Court term. For a contrasting view on United States v. Skrmetti, please see this piece by Craig Konnoth.

The majority opinion in United States v. Skrmetti is both measured and bold. By its terms, the decision leaves for another day questions like whether the court’s 2020 decision in Bostock v. Clayton County applies outside of the hiring and firing contexts governed by Title VII and whether transgender individuals constitute a quasi-suspect class. Yet the decision is also a clear victory for the legal point of view that a reference to sex does not necessarily trigger heightened scrutiny. And the way the court reaches that conclusion – by reaffirming that the biological differences between men and women matter – suggests that a majority of the court may view some lines as constitutionally permissible, such as laws that separate bathrooms and sports based on sex.

In 2023, Tennessee enacted a bipartisan law (known as SB1) that prohibits health care providers from performing surgeries or administering puberty blockers and cross-sex hormones on minors “for the purpose of: (A) [e]nabling the minor to identify with, or live as, a purported identity inconsistent with the minor’s sex; or (B) [t]reating purported discomfort or distress from a discordance between the minor’s sex and asserted identity.” The question before the Supreme Court in Skrmetti was whether SB1’s purpose-based prohibition on puberty blockers and cross-sex hormones violated the equal protection clause.

A 6-3 majority of the Supreme Court answered that question no. Chief Justice John Roberts’ opinion (joined in part or in whole by Justices Clarence Thomas, Samuel Alito, Neil Gorsuch, Brett Kavanaugh, and Amy Coney Barrett) concluded that SB1 does not classify on any basis that would warrant heightened review. Rather, the court found that SB1 classifies based on age (because it applies only to minors) and based on medical use (because it prohibits drugs and hormones for the purpose of treating gender dysphoria and related conditions).

The ACLU challenged the law in federal court on behalf of three families, and the Biden administration intervened. The plaintiffs argued that SB1 classifies based on sex because its medical use prohibitions reference sex and because application of SB1 turns on sex. The court disagreed.

First, the court firmly repudiated the plaintiffs’ argument that any time a statute or regulation references sex, it is subject to heightened scrutiny. The Biden administration pushed the view that, because SB1’s prohibitions “cannot be stated without referencing sex,” they are “inherently based upon a sex-classification.” In no uncertain terms, the majority wrote that the court “has never suggested that mere reference to sex is sufficient to trigger heightened scrutiny.”

This makes sense. As Chief Judge Jeffrey Sutton’s opinion for the U.S. Court of Appeals for the 6th Circuit explained, such a view would all but invalidate scores of commonsense laws – laws protecting pregnancy or regulating prostate cancer, for instance. It would also turn equal protection jurisprudence into a word game. Laws regulating pregnancy would be permissible, but those providing protections to women who were pregnant would be subject to heightened scrutiny. The Supreme Court has long held that semantics do not control the equal protection analysis. As the majority wrote in Tuan Anh Nguyen v. INS, “[j]ust as neutral terms can mask discrimination that is unlawful, gender specific terms can mark a permissible distinction.”

The court’s rationale for holding that a law referencing sex does not classify based on sex under the equal protection clause is also a potential harbinger of how the court may look at future cases. The court relied on the commonsense principles that biological differences between men and women both exist and matter. The majority recognized that “[s]ome medical treatments and procedures are uniquely bound up in sex.” The court further explained that, according to the Food and Drug Administration, “biological differences between men and women” may contribute to drug efficacy and safety differences. As Justice Ruth Bader Ginsburg famously explained in United States v. Virginia, “[p]hysical differences between men and women” not only exist but are “[i]nherent” and “enduring.”

This holding bodes well for the defenders in future challenges to statutes separating intimate spaces or sports based on sex. Just as “biological differences between men and women” may lead to different drug efficacy, biological differences between men and women may lead to physical advantages and privacy concerns.

The Skrmetti majority rejected the Biden administration’s view that biological differences between men and women come into play only during a court’s application of heightened scrutiny. While the Biden administration acknowledged that “‘[p]hysical differences between men and women may sometimes justify legislative reliance on sex,” it argued that those considerations were relevant only to whether a law survives heightened scrutiny. The court disagreed, holding that those considerations were relevant to whether the line drawn by SB1 classified based on sex at all.

Second, the court rightly rejected the argument that SB1’s medical use classification “turned on” sex. The plaintiffs argued that SB1 prohibits certain treatments for minors of one sex while allowing those same treatments for minors of the opposite sex. The majority pointed out the flaws in this framing, explaining that SB1 turns on the underlying “medical concern.” And SB1 does not prohibit conduct for one sex that it permits for the other. Rather, “a healthcare provider may administer puberty blockers or hormones to any minor to treat a congenital defect, precocious puberty, disease, or physical injury” (emphasis added). And a healthcare provider may not administer puberty blockers or hormones to any minor to treat gender dysphoria, gender identity disorder, or gender incongruence. The distinction in SB1 thus turns on medical purpose, not sex.

Further, the majority’s opinion makes one wonder whether the “turns on sex” inquiry is the right one to begin with. At times, the majority suggests that the proper equal protection standard is whether the statute or regulation prescribes one rule for women and a different one for men. “For reasons we have explained,” the court wrote, SB1 “does not prohibit conduct for one sex that it permits for the other.” Rather, “no minor may be administered puberty blockers or hormones to treat gender dysphoria, gender identity disorder, or gender incongruence; minors of any sex may be administered puberty blockers or hormones for other purposes.”

The majority also rejected the plaintiffs’ argument that Bostock’s but-for causation test applied to SB1. Saving for another day the question whether that test can be imported into the equal protection clause (three justices rejected that idea), the majority found that the but-for test was unmet. That causation standard directs the court “to change one thing at a time and see if the outcome changes. If it does, we have found a but-for cause.” That test, the court opined, was meant to ferret out situations where “the employer has penalized a member of one sex for a trait or action that it tolerates in members of the other.” It was not met in Skrmetti, the majority found, because changing a minor’s sex does not alter the application of SB1.

The majority also rebuffed the plaintiffs’ argument that the statute classified based on transgender status. Alito’s concurrence explained that he would hold that transgender individuals are not a quasi-suspect class. Barrett, joined by Thomas, concurred to explain her view that establishing a new quasi-suspect class was nearly impossible due to a demanding standard of immutability and discrimination enforced by law – neither of which applied to transgender status.

The majority then held that SB1 “clearly” met the rational basis standard. The Tennessee Legislature had rationally determined that administering puberty blockers and hormones to minors “can lead to the minor becoming irreversibly sterile, having increased risk of disease and illness, or suffering from adverse and sometimes fatal psychological consequences.” The majority also found it rational for Tennessee to conclude that the drugs and hormones were experimental in nature and unsupported by high-quality medical studies. So too for the Legislature’s concern that minors may lack the maturity to appreciate and evaluate these risks and its finding that discordance between sex and gender “can be resolved by less invasive approaches that are likely to result in better outcomes for the minor.”

Finally, the majority highlighted the divergent institutional competencies of courts and legislatures. The Constitution entrusts improvident decisions to “the democratic processes,” the court wrote. And there was evidence to suggest that the Tennessee Legislature’s decision to protect minors from these drugs was not improvident. “Recent developments” in the scientific evidence regarding puberty blockers and hormones underscored the need for “legislative flexibility.” Specifically, an independent UK report had characterized the evidence used in support of these drugs and procedures as “remarkably weak.” Thus, SB1 was rationally related to “the State’s objective of protecting minors’ health and welfare.”

At day’s end, the court’s ruling is a measured but robust win for the state’s ability to protect its minors from risky drugs and procedures. It also signals that a majority of the Supreme Court thinks that some sex-based lines are constitutionally permissible. We’ll need to wait for a future case to see exactly how these principles will play out.