Records show that Ohio has enough of its execution drug to complete seven of its 10 scheduled lethal injections.
The expiration of the supply of pentobarbital in September 2013 will force the state to either find a different version of pentobarbital or switch to another drug altogether.
The drug's manufacturer prohibits its use for executions.
Prisons agency spokeswoman JoEllen Smith tells The Associated Press the department will be working with state pharmacists and the attorney general's office to address the issue.
Prisons director Gary Mohr testified in federal court in March that an altered version of pentobarbital or a supply imported from overseas would not necessarily violate the prison's execution policies.
Other states are also facing possible shortages of pentobarbital, and Missouri switched to another drug altogether earlier this year.