Forensic toxicological analyses of drugs in tissues in formalin solutions and in fixatives.

•Psychoactive drug levels were examined with formalin-fixed human tissues.•Tissues of ante- and post-preservation of multiple terms and fixatives were used.•Drug levels did not necessarily show further decreases with extended storage.•Proportion of drugs remained within tissues differed between liver and kidney.•S-oxide compounds of assayed drugs were generated in formalin storage of liver.