Question

A drug user who has developed a high tolerance to a drug could take an overdose large enough to cause death.

Answer 1

If you're wanting to know true or false, then yes they can.

When they develop a tolerance for it, they don't get the same effects as the did before the tolerance, so then they'd take more of it to get those effects back. If they keep having to increase the amount, they eventually take too much, overdose, and in a lot of cases, die.