The former Strikeforce welterweight champion was tested following his defeat to Carlos Condit in a bout for the UFC’s interim title in the same weight class on February 4 in Las Vegas.
The suspension has been dated retroactively from that day, despite Diaz’s attorney Ross Goodman arguing that the test showed inactive metabolites, not the parent drug.
Diaz submitted a urine test after the unanimous decision defeat which contained 25 nanograms of marijuana metabolites, with the NSAC regarding anything above 15 nanograms as a positive test.
While marijuana metabolites are a byproduct of the drug, marijuana is not an out-of-competition banned substance by the NSAC.
NSAC chairman Raymond Avansino said: "I think that the standard test we use in Nevada is not likely to be changed in the future.
“We test for marijuana metabolites. That's the manner we formally test. We are obligated to adhere to our standards."
The decision comes at the end of a four-hour hearing which concludes a long legal conflict between the commission and Diaz.