Mouse poison can work on rats.
However mouse poison is less toxic for rats than it is for mice so if you use mouse poison for rats it can take more mouse poison to kill the rats.
When killing rats it's best to buy some actual rat poison that is formulated and made strong enough to kill rats.
The mouse and rat poison will not kill rats or mice instantly but instead the mouse poison and rat poison takes time and kills the rats and mice slowly.
The rat and mouse poison causes internal bleeding and prevents the mice or rats blood from clotting so that they die of internal bleeding.
So you might see the same rat or mice out for a few days before they actually die.
The best way to kill a rat or mice is to kill it instantly using rat traps or mice traps.