What is the test for a prison official to be deliberately indifferent in their response to a serious medical need?

For a prison official's response to a serious medical need to be deliberately indifferent, the official must "'know[] of and disregard[] an excessive risk to inmate health.'" Peralta v. Dillard, 744 F.3d 1076, 1082 (9th Cir. 2014) (en banc) (quoting Farmer v. Brennan, 511 U.S. 825, 837 (1994)). "[T]he official must both be aware of facts from which the inference could be drawn that a substantial risk of serious harm exists, and he must also draw the inference." Farmer, 511 U.S. at 837.

It is well established that "a mere difference of medical opinion . . . [is] insufficient, as a matter of law, to establish deliberate indifference." Toguchi v. Chung, 391 F.3d 1051, 1058 (9th

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