The drugs are cheaper in Canada and Mexico because the government imposes a lower price by law. As long as the required price is higher than the cost of manufacturing the drug, pharmaceutical companies will always sell the drug at the government imposed price. That means the United States, which doesn't force this price on the pharmas, ends up subsidizing the cost of R&D for Canada, Mexico, and other countries with such laws in place. But what happens if the U.S. follows the lead of those other countries and imposes price restrictions? It will be impossible for pharmas to recoup their expenses so EVERY new drug will end up losing money. If every new drug becomes a losing proposition, no one will invest in their development.