A substance called rT3 blocks your body's active thyroid hormones from working properly by taking their place on cellular receptors. This prevents your cells from getting the energy signals they need, which ultimately slows down your metabolism.

Our current analysis shows that the evidence we have reviewed leans toward inactive reverse triiodothyronine, or rT3, slowing down your metabolic rate by blocking thyroid hormone receptors. We analyzed the available data and found that 1.0 studies support, 0 studies refute. [1] What we have found so far suggests that rT3 acts like a placeholder in your cells. Your body normally uses active thyroid hormones to send energy signals to your cells. When rT3 takes the place of these active hormones on cellular receptors, it blocks the signals from getting through. This means your cells receive fewer energy cues, which our review indicates may lead to a slower metabolism. The evidence we have reviewed leans toward this blocking mechanism being a key factor. We want to be clear that this is a partial view. Our analysis is based on the limited data available right now. As more research becomes available, our understanding will likely improve. We do not have enough evidence to say this happens in every situation, and we cannot claim it is a fixed rule. The evidence we have reviewed leans toward this mechanism, but we are still gathering more information to see how it fits into the bigger picture. In everyday terms, think of your thyroid hormones as keys that unlock energy production in your cells. rT3 acts like a broken key stuck in the lock. When it sits in the lock, the real keys cannot turn, and your body gets less energy. If you are trying to manage your weight or energy levels, it may help to talk with a healthcare provider about how your thyroid function is working. Monitoring your levels and adjusting your routine based on professional advice is a practical step you can take while we continue to track new findings.