YES it is..I did in the summer, mostly because I was bored. And I found out it can be very bad for you. If you do it to much it can cause prostate cancer. If you are not aware of you anatomy(im sure you are the outside) but like go to google so you can better understand what im going to tell you. You should know that sperm is made in the testes. Well once its made it travels in then out of your prostate. Your prostate (along with cowpers glands) add chemicals to the sperm. Your prostate gives it this chemical which helps it survive in the womens vagina.(it adds this chemical because the vagina is acidic) Without the chemical the sperm would not survive. After a while your prostate is all like, holy shit I need to make more of this chemical for all of the sperm. So your prostate begins producing a lot more of this chemical to compinsate for all the sperm that is traveling through, so to do this it needs to become larger. Soo obviously the cells are dividing(mitosis) faster(uncontrolled mitosis) and you now are developing cancer. Cancer is when cells in our body begin to produce way to fast. Make sense?. If you dont understand anything pm or just leave it in this topic.
Soo I would say the only thing you can do now is not do it 3 times a day. I think about 4 times a week is healthy. Yeah I know, this can be hard to do.

Hope this was a help.