My pharmacist says that the problems are most likely to occur if you are switching from one brand to another. Even generics are made by different companies. So what you get one month, made by company A, is within a certain level of change from the original brand. Then, you get a generic made by company B the next month. Company B's pill is also within X percentage of the original, but may be quite a bit different than Company A'a. One could be over the original brand, the other could be under. So if the tolerance is 3%, and A is 3% more than the original brand, then B is 3% under the original brand, well, you get a difference of more than 3%. The numbers are ones I picked to illustrate the problem.
My pharmacy tries to make sure they can buy a medication from a company for at least a year. They say the problems are most often noticed in birth control pills and seizure medications. NOT areas I would want to experiment with.
Susie