Since I'm not a chemist, I cannot attest to the quality of U.S. prescription drugs compared to those from India.
I can say that Alinia (nitazoxanide) by prescription costs $30 for a 500 mg tablet. Whereas from India a 500 mg tablet cost $.25. The standard dosage is two 500 mg tablets per day for a cost of $60 by prescription vs. 50 US cents for the India drug.
I have taken drugs from Thailand, Vietnam, India, Mexico and U.S. I have not experienced a problem with any of them.