Yes, we do.
It’s something a lot of people are not sure about, but also something that we are legally obliged to do. We can’t give potential medicines to people without understanding what they might do to them as side effects. We do that by testing on animals (rats, mice, then dogs), and also simulating on a computer. The human body is far too complicated for us to fully understand without those.
There are very strict rules though, that limit the number of animals we can use. We always avoid animal testing if we can.
I have seen the animals that are being tested on, and they live a happy life. The dogs run towards you and want to play, they don’t seem worried at all. As soon as the vets see any signs of side effects they stop giving that drug to the animal, so the animal is never very uncomfortable.
People who love animals are happy with the way the animals are treated, and happy in a job that allows that.