When two specific drugs are taken together, they can damage liver cells in mice by disrupting their energy factories and causing cell death — but each drug alone, at the same dose, doesn't do anything harmful. This means the danger only shows up when both are present.

When mice liver cells are exposed to two specific drugs together, they produce a harmful chemical that damages the cell’s energy factories, causing the cells to die. But if you add a substance that neutralizes that harmful chemical, you can stop the cell death.

A drug called efavirenz can block a key energy process in mouse liver cells at a specific dose, and while it doesn’t hurt the cells by itself, it makes them much more likely to get damaged when combined with another drug called isoniazid.

A chemical called hydrazine, which the body makes when it breaks down a tuberculosis drug, can damage liver cells by disrupting energy production in mitochondria. When combined with another drug (efavirenz), this damage gets worse—but if you stop hydrazine from forming, the liver cells don’t die.