What is the current state of the law on drug usage as impeaching evidence?

absence of manifest abuse, upon a finding that its decision was palpably arbitrary, capricious and patently absurd. [Citations.]" (People v. Jennings (2000) 81 Cal.App.4th 1301, 1314.)

The state of the law on drug usage as impeaching evidence was summarized in People v. Hernandez (1976) 63 Cal.App.3d 393. The court held that "proof of a narcotic addiction, standing alone, is inadmissible to impeach the credibility of a witness and that such evidence is not only collateral thereto but highly prejudicial." (Id. at p. 405.) Such evidence is inadmissible unless there is evidence that "tends to show that the witness was under the influence thereof either (1) while testifying, or (2) when the facts to which he testified occurred, or (3) that his mental faculties were impaired by the use of such narcotics. [Citation.]" (Ibid., cited with approval in People v. Panah (2005) 35 Cal.4th 395, 478.)