If you’re taking the time to read this post, it is likely that you are an up-and-coming international cannabis company like https://www.koalitymedicinals.com/ that seeks to sell your medicinal cannabis product for medical purposes in the United States of America. While this is no easy task, the good news is that it is more possible today than it has ever been. The difficulty your company will experience in importing the product will depend greatly on two factors: the chemical construction and medicinal value of your product with whom you seek distribution.
Before you can seek distribution, your cannabis product must follow FDA protocol and yield favorable results that eventually lead to FDA approval. This will depend greatly on the chemical construction of your product. There are five major cannabinoids in medical marijuana that relieve symptoms. Each one produces different psychological and physical effects.  The balance of these effects and the total medicinal value and risk of abuse is weighed by the FDA when ruling on approval.
The good news is that there is now a company that will import your international cannabis product for research and trials that could eventually lead to approval and ultimately commercial distribution. As of December 3rd, 2015, the Department of Justice published in the Federal Register a notice of registration for Catalent CTS, LLC., that grants them permission to import finished pharmaceutical marijuana products containing cannabis extracts in dosage form for clinical trial studies that could lead to the sought after FDA approval. 
The uprising of companies such as Catalent CTS wouldn’t have been possible without various memorandums from the DOJ issuing guidance regarding marijuana enforcement in states where medicinal or recreational marijuana is legal under state law. On October 19th, 2009, David W. Ogden, Deputy Attorney General, issued a memorandum for federal prosecutors to use their discretion in prosecuting individuals and caregivers who violate the Controlled Substances Act (“CSA”) but adhere to state marijuana laws. The justification for this lax enforcement was efficient and rational use of limited federal resources.  Mr. Ogden made sure to clarify that this type of prosecutorial discretion was only to be exercised when the following characteristics were not present:
“unlawful possession or unlawful use of firearms; violence; sales to minors; financial and marketing activities inconsistent with the terms, conditions, or purposes of state law, including evidence of money laundering activity and/or financial gains or excessive amounts of cash inconsistent with purported compliance with state or local law; amounts of marijuana inconsistent with purported compliance with state or local law; illegal possession or sale of other controlled substances; or ties to other criminal enterprises.” 
In 2013, the new Deputy Attorney General, James M. Cole, reiterated his predecessor’s memorandum. Mr. Cole also further clarified that just because a business is sizable and is for-profit should not sidestep the discretion that Mr. Ogden outlined in his 2009 memorandum.  That is, as long as the business is not in violation of any of the above-listed characteristics from the 2009 memo. 
So as long as you are using an authorized, reputable, transparent company to conduct trials and eventually market your product, you at least have a chance (even if it is small) to market your medicinal marijuana product in the U.S. Which is a hell of a lot better than your prospects would have looked 5 years ago.