endometriosis
"I've been on Norethindrone for probably 2 years. I never have periods unless I go *beyond* 3 hours after my usual time slot for taking it. You should take it within 1-2 hours same time every night. What I can say is I love having no periods. 
However, I have little to no desire for sex. If you want to be celibate, take this pill and you won't care about sex, haha. 
So, I can't say I take it to prevent pregnancy. Symptoms I seem to have often: Anxiety (though I've been on pill 24 years, all different brands, always had anxiety). I also have TMJ, depression and no interest in activities. I'm very lazy and a heavy smoker. Mood swings OFTEN. Quick temper. Wait? Maybe this is from the celibacy. "