If you’re a guy – or even just friends with a guy – and on the Internet, you may have noticed that testosterone discourse is everywhere. There’s Defense Secretary Pete Hegseth announcing testosterone screenings for soldiers, Joe Rogan discussing hormone therapy, and influencers discussing high- and low-T levels. Those levels affect more than just sex. They also affect metabolism, bone health, muscle mass, red blood cell production and brain function. NPR science reporter Will Stone took a deep dive into it all: What deficiency looks like in men, what doctors recommend and what the research says about who actually needs testosterone replacement therapy.Interested in hearing more reporting on popular science topics? Email us what you’d like us to cover at shortwave@npr.org.Support public media with NPR+ and enjoy perks for over 25 podcasts like this one. This show’s perks include sponsor-free listening. Learn more at plus.npr.org.