Thirty-three-year-old Yokamon Hearn is set to die for a 1998 murder in Dallas. He would be the sixth person put to death in Texas so far this year.
Last week the state agreed to adopt the one-drug protocol for executions.
Jason Clark is with the Texas Department of Criminal Justice.
"We changed the protocol July 9th. The second drug that we had in our supply expired and we were unable to obtain a new shipment. So by implementing this change to the protocol, we'll be going to a one-drug sequence."
That drug, pentobarbital, is given in a big enough dose, 5 grams, to cause death. It's an anesthetic and the person becomes unconscious before death.
"In that three-drug sequence, if you took away the other two, that first drug is lethal in and of itself. So, nothing will really change as far as the execution being carried out."
Hearn has appealed today's execution. His attorneys say he's mentally impaired. Several appeals courts have rejected previous attempts to halt the execution.