I'm taking Cerazette, and haven't had my periods in 3 years...
My gyn told me that one day, my body will refuse to go on with this pill, and I'll experience permanent spotting. When that happens, I'll have to switch to a 'normal' (21 days) pill. But as long as it works, I keep my Cerazette!
I experienced no side effect at all, so I highly recommand it! But it doesn't work so well with everybody: some women have constant spotting from the beginning, others still have light periods from time to time. And some lucky girls like me are totally rid of their periods