That's a complex subject. Some Libertarians would say they are. Others would say not.
How can anyone suggest government protected monopolies are not interfering with a "free" market?
Dean Baker, "The Reform of Intellectual Property", Post-Autistic Economics Review, issue 32.
"The economics profession has devoted vast amount of research and textbook space to proving the inefficiency of various forms of protectionism.
"The basic story in this work is that protectionism causes the price to exceed the marginal cost of production.
"All of this work is entirely applicable to patents and copyrights, except the impact is at least an order of magnitude larger than with most instances of protectionism in international trade.
"While tariffs and quotas rarely raise the price of goods by more than 30 or 40 percent,
patents on prescription drugs typically raise the price of protected products by 300 to 400 percent, or more, above the marginal cost."