Brooksby, who achieved his highest career ranking of 33rd last year, previously accepted a voluntary provisional suspension and his sanction will be backdated to July 5th. The sanction will end on January 4th, 2025, according to the ITIA.
He previously told the AP that he had never failed a drug test or taken "bad substances".
The ITIA said that Brooksby accepted the first and third missed tests but disputed the second one.
Missing three in a 12-month period can constitute an anti-doping rule violation, according to the ITIA. Brooksby has 21 days to appeal against the decision to the Court of Arbitration for Sport (CAS).
"The whereabouts programme is a vital tool in maintaining a clean sport," ITIA CEO Karen Moorhouse said in a statement.
"No one wants players to fall foul of the rules in this way."
