07-26-2015, 10:14 PM
Andy if you're talking about buying a medication in the U.S. with a valid prescription from a licensed pharmacy, there is absolutely no difference. The generics must contain the exact same amount the of active ingredient. This is regulated by the FDA and and strictly enforced. If the generics do not contain the exact same amount of active ingredient, the FDA would shut them down.
From the FDA:
What standards do generic drugs have to meet?
Health professionals and consumers can be assured that FDA approved generic drugs have met the same rigid standards as the innovator drug. To gain FDA approval, a generic drug must:
  contain the same active ingredients as the innovator drug(inactive ingredients may vary)
  be identical in strength, dosage form, and route of administration
  have the same use indications
  be bioequivalent
  meet the same batch requirements for identity, strength, purity, and quality
  be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products
http://www.fda.gov/Drugs/ResourcesForYou...100100.htm
From the FDA:
What standards do generic drugs have to meet?
Health professionals and consumers can be assured that FDA approved generic drugs have met the same rigid standards as the innovator drug. To gain FDA approval, a generic drug must:
  contain the same active ingredients as the innovator drug(inactive ingredients may vary)
  be identical in strength, dosage form, and route of administration
  have the same use indications
  be bioequivalent
  meet the same batch requirements for identity, strength, purity, and quality
  be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products
http://www.fda.gov/Drugs/ResourcesForYou...100100.htm