In my case, I’m allergic to the base used in the manufactured version of a drug my doctor prescribes. Not only do I have to pay it out of pocket, it’s very expensive. In addition, I can’t fight with the insurance company about the necessity without going back to trying the manufactured drug and going through all of the problems again. Why? Because the allergy was discovered years ago and I no longer have those records. Many years ago, no one thought to get their records and some doctors wouldn’t give them to the patient. After many moves, and many doctors retiring and moving themselves, the track is lost. It’s beyond me why I’d make up something like that when it would save me time and money to use the more easily available product, but the insurance company wants total control. That comes right up there with making people try lower cost drugs and generics. My MIL had a reaction to the generic of her blood pressure medication, due to a sensitivity to one of the ingredients. Food colors, preservatives, and other things can cause legitimate reactions.