I have these two different packs because I switched pharmacies. I was on the yellow pills first and still have 2 packs, my pharmacy gives out 3 packs at a time. When I went to my new pharmacy the order was ready and i got the green pills. the green pills expire before the yellow pills. I'm wondering if it's ok to switch back and forth SINCE they both have norethindrone 0.35mg as the active ingredient. the exact same active ingredient, the only mini pill on the market in the US. the inactive ingredients may differ.