On Wednesday, US Secretary of Defense Pete Hegseth announced an initiative to screen US military members for low testosterone. “The modern battlefield is brutal and unrelenting,” he said. “It requires and demands maximum psychological and mental readiness. And by addressing these health markers early, we’re keeping you on the leading edge of lethality.” Troops found to be deficient in the screening, Hegseth said, would be offered testosterone therapy—which, he promised, would make them better warriors. “It’s about restoring and optimizing your natural capabilities,” he said, “protecting your longevity, ensuring you have the biological foundation required to sustain the fight.”

The idea of a widespread testosterone deficiency—”Low-T” among the extremely online—is having a moment. Over the last few years, influencers have made a cottage industry of telling men that their testosterone levels are low and selling them testosterone therapy. Consumer research firms estimate the market value for testosterone replacement therapy at around $2 billion; that number is expected to increase by a third by 2033.

Earlier this year, the Guardian reported on a recent study of low-T influencers by Emma Grundtvig Gram, a public health researcher at the University of........

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