Viagra?

I had posted previously looking for advice about my husband having performance anxiety. His doctor has prescribed him viagra for when it's needed, which has been working thankfully. However, I was just reading that some fertility doctors believe that viagra causes fertility issues, something about it weakening the head of the sperm or something? I didn't fully understand what they were saying, but that's what it sounded like to me.

I guess my question is, have any of you ever heard of this? Or have any of you had issues from viagra or had success with it? It's making me so worried that we're never going to conceive if viagra is the only way we can have sex.

Edit for clarification: He is able to have sex just fine any other day. But once it's time to ttc, he has the problem.