Scientists have discovered a new biological mechanism that explains how certain medications and environmental chemicals can influence the balance of sex hormones in the human body.

The study, published in the journal Basic & Clinical Pharmacology & Toxicology, shows that many substances can alter hormonal balance through a previously unknown molecular pathway.

At the center of the discovery is the so-called PXR receptor — a sensor protein that helps the body detect and process various chemical compounds, including drugs. For a long time, it was believed that its main function was related to liver activity and detoxification. However, the new research showed that this receptor also affects the production of a special protein called SHBG (sex hormone–binding globulin).

This protein plays a key role in regulating hormonal balance. It transports hormones such as testosterone and estrogen in the bloodstream and determines what portion of them remains “free” and able to actively affect body tissues. When SHBG levels change, the availability of sex hormones to cells also changes.

To test this mechanism, researchers conducted an experiment involving healthy volunteers. For one week, participants were given the antibiotic rifampicin, a substance known to be a strong activator of the PXR receptor. The results were quite striking: SHBG levels in the blood nearly doubled in almost all participants. In men, the total level of testosterone also increased.

Additional laboratory experiments on liver cells confirmed the causal relationship. When the activity of the PXR receptor was blocked, the increased production of SHBG disappeared. This allowed scientists to confirm the existence of a new mechanism — the so-called PXR–SHBG–testosterone pathway.

According to the researchers, the discovery is important because the PXR receptor can be activated by a wide range of substances — from medications to components of food and environmental chemicals, including pesticides, plastic additives, and flame retardants.

This means that such substances may indirectly influence the human hormonal system by altering the levels of available sex hormones. Understanding this mechanism could help scientists more accurately predict the hormonal effects of medications and the potential health impact of environmental chemicals.