A "genuine" president would have issued hundreds of thousands of pardons for drug "crimes" by this point in his presidency. Obama is just another politician.
Andrew Johnson pardoned everyone who fought for the Confederacy, other than Jeff Davis and a few other bigwigs. Sure, armed insurrection is a less serious crime than getting high, but I think the precedent stands.
Strictly speaking however "precedent" doesn't apply to pardons since they are a power specifically granted the president by Article II, Section 2 of the United States Constitution. Precedents are important in courts, so if e.g. the Supreme Court had previously ruled that pardoning pot smokers is unconstitutional then that precedent would be relevant. My impression is that the courts don't want to touch pardons, which is only right, since the point of putting them in the Constitution was to give the executive the ability to rein in the vindictiveness of the legislative and judicial branches. I expect that if Congress passed a law attempting to restrict the use of pardons, even the most conservative jurist would toss that shit right out of court.
