In certain human cells, the more creatine builds up inside, the less the cell makes on its own — like a built-in thermostat that senses creatine levels and turns down production when there's enough.

In certain human cells, how much creatine is inside the cell controls a specific gene switch, no matter how the creatine got in—meaning the cell cares about its internal supply, not where it came from.

Scientists made a tool in lab-grown cells that lights up when creatine is present, so they can quickly test how well different drugs or substances affect creatine levels inside cells.

Creatine gets into human cells in two ways: one is like a precise lock-and-key system that works well at low levels, and the other is a more general process that kicks in when there's a lot of creatine around.