There's another big problem too Knight. In America, many people see multiple doctors. For example, a cardiologist and a general practitioner (family doctor). The doctor may not know or even care that you are seeing another doctor. Now, they normally get you to file a form stating the meds you are taking. However, that can change from time to time, and the patient may forget to inform the doctor.
Well, you know what happens after that. Unless you are using the same pharmacy, they may not let you know there will be drug interactions.
‘Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.’ Sir Winston Churchill