What is the standard of review for denial of a proposed jury instruction of an addict-informer?

This circuit has yet to resolve the split in the appropriate standard of review for denial of a proposed jury instruction. See United States v. Whitehead, 896 F.2d 432, 434 (9th Cir.1990). In this case, however, the standard of review does not affect our decision.

An addict-informer instruction is appropriate when the witness is an addict. United States v. Ochoa-Sanchez, 676 F.2d 1283, 1289 (9th Cir.), cert. denied, 459 U.S. 911 (1982). The instruction, however, is "unnecessary in several situations, including: (1) when the addiction is disputed; (2) when the defense adequately cross-examines the witness about the addiction; and (3) when another cautionary instruction is given." Id. (citations omitted).