I wasn't familar with the name Kelnor so I looked it up and found that the other names it goes by.

Zovia 1/35e, Demulen 1/35-28, Kelnor 1/35-28, Kelnor 1/35, Zovia 1/50e, Demulen 1/50-28, Demulen 1/50-21

I haven't taken any of them so I really can't help with your question sorry. The only thing I can say is that when switching BCP women need to take them for at least 3 months before their body gets accustomed to it.

I have taken all of these, first Demulen for years then the generic Zovia, now the pharmacy gives me Kelnor in place of Zovia. Never had a problem with Demulen or Zovia but since taking Kelnor for months it really made my cycles messed up. You normally get your cycle on 4th week of pills, now with this new pill I am getting it 1st week of cycle or sometimes the 4th week, I never know???? I discussed with my doctor and she wrote up ZOVIA ONLY, do not substitute. That is the only side effect I have with itl