Cite one, just one, reliable source for this assertion.
Dr. Burke, president of the American Historical Reference Society and a consultant for the Smithsonian Institute, counted seven early presidents as cannabis smokers: George Washington, Thomas Jefferson, James Madison, James Monroe, Andrew Jackson, Zachary Taylor and Franklin Pierce. “Early letters from our founding fathers refer to the pleasures of hemp smoking,” said Burke. Pierce, Taylor and Jackson, all military men, smoked it with their troops. Cannabis was twice as popular among American soldiers in the Mexican War as in Vietnam: Pierce wrote to his family that it was “about the only good thing” about that war.