OK, here is the scoop. There is no law in MA (I live in Boston, MA) stating that pharmacies HAVE to replace the branded product with the generic equivalent. There are however, a few other laws that address this issue. By law, a script can be changed with the consent of 2 out of the 3 parties involved:
1. The Doctor
2. The Pharmacist
3. You, the patient
IF you and the doc decide to change the script, or the doc and the pharmacist, or the pharmacist and you - then it is kosher.
Bear this in mind... Although there is not an official law saying that the pharmacy HAS to change over every script to a generic... there are corporate guidelines that they are made to follow. CVS, for example makes it much more worthwhile to the Pharmacist to dispense generics. The Pharmacy makes FAR more profit pushing the generic over the branded product, and in turn passes this along to the Pharmacist.
As far as equivalency is concerned, this is an argument that has raged since the enception generics. Some say that there is a difference with the quality, and others state that they are absolutely identical. I stand somewhere in the middle. Working myself for a Biotech firm and being in this industry for the past 5 years, I can honestly say there IS a difference with some meds - but I do not feel that it would be fair to say that all generics are less efficacious. Drugs like inhalable cortico-steroids (ventilin, albuterol, Aerobid, etc.) have generic equivalents that are notorious for not providing the same degree of release from asthma (ie. the patient has to take 3 puffs of the generic, whereas they only need 1 puff of the branded product. Also, hormonal drugs that have doses that need to be titrated up in a patient very carefully are often prescribed as DAW (Dispense As Written) or NSA (No Substitution Allowed) because many physicians find that the dosage precision and consistency with the generic product is not up to par. Synthroid is a perfect example of this, as it is still widely used, despite the fact that it has gone off patent years ago.
Things like binders, delivery mechanisms and the quality of other non-active ingredients may also vary with generics - and this may or may not deduct from there efficacy/tolerability. I know that generic Norco (Hydrocodone/APAP) lacks the waxy matrix binder that the branded product has. This ironically, proved to be an advantage in my case, as the generic, powdery, non-waxy pills were more easily crushed up and consumed... where as this could not be done with thew waxy branded Norcos.
As far as good old fashioned Alprazolam, I wouldnt expect there to be a tremendous difference. Although it is possible, it might also just be an issuee of tolerence building up or simply a placebo effect.
SG