In light of the radiation poisoning risk from Jaegers that used nuclear reactors, Metharocin was given to Rangers as a preventive measure alongside the Jaeger's initial radiation shielding and even afterwards when the Pan Pacific Defense Corps recalled these Jaegers in order to improve shielding for future Jaegers.
Rangers are required to take Metharocin on a daily basis given their proximity to their Jaegers, inside or outside of the machine. Metharocin, however, is not a one-hundred percent effective countermeasure against preventing cancer-related illnesses. Notable cases, such as Tamsin Sevier and Stacker Pentecost, show that despite taking the medication, their prolonged exposure to Coyote Tango's nuclear reactor resulted in the development of terminal cancers.
- Tendo popped open a small tin and handed Raleigh a pill. “Metharocin,” he explained. “New precaution. It’ll shield you from radiation while you’re out of your suit.” Pointing up at Gipsy Danger’s torso, he added, “Exposed core is still fuel rod.” Raleigh took the pill. Pacific Rim: The Official Movie Novelization, page 92