Listen to a doctor at the Huerta Memorial Hospital on the Citadel. The doctor is standing on the left as you exit the elevator.
Alternatively, you can acquire the mission without overhearing the doctor first by finding the formula in N7: Cerberus Lab. This second way of acquisition is possible even before the finishing the mission Priority: Palaven
Note: This mission must be completed before completing Priority: Tuchanka as it will be the last opportunity for the player to visit the Citadel before Priority: The Citadel II, after which it will no longer be available.
During the mission N7: Cerberus Lab, access a console to reveal a "failed" Cerberus experiment. While it produces a breakthrough for hanar, it won't do anything for humans. After completing the mission, head back to the hospital and hand the formula over to Dr. Ravin.