I'm taking a hormone patch to help with osteoporosis. it says to change it twice a week on the same days (3 days and then 4 days). was this system created for convenience only? if there is enough hormone for 4 days, can i just change it every 4 days?

I think your pharmacist can best answer this question.

If you are using a bi-weekly Estradiol patch, e.g., Alora, Minivelle, or Vivelle-Dot the patch is usually replaced twice weekly (every 3 to 4 days). It is just easier to create a recurring schedule when done this way, so that you are reminded to change your patch on the same particular days of the week. Compliance is likely to be better. Other than that, it is perfectly fine to do once in 4 days.