How Safe Is Taking Norethisterone Tablet For Irregular And Heavy Periods?

I'm perimenopausal and have just started taking norethisterone tablets due to long (up to 30 days sometimes) irregular and recently very heavy periods at times. I've been told it's O.K. to take them for 3-4 weeks but now worried when I stop that my period will be uncontrollable. Would reducing the tablets over the time help?