Indeed. This is why the drug passed phase 1 (safety) trials when it was first approved in 1992 for treatment of prostate enlargement. Moreover, it subsequently passed additional rounds of clinical trials for the hair loss indication in 1998, and has been involved in more than 30 different clinical trials overall.

Now, I'm not going to argue that there can't be rare side effects that are only discovered with time. I'm also not going to claim that the original trials were perfect, or that research into the question isn't justified. But you're trying to assert that they didn't test for safety, and that's just factually incorrect.