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Body fluids and tissues in eight doxepin (Dox)-related deaths were investigated in order to prove whether the individual concentration of Dox, the concentration sum of parent drug and its active metabolite N-desmethyldoxepin (NDox) or the concentration ratio Dox/Ndox valuably contribute to making a cause of death determination. Individual case histories were shortly described. Dox and NDox concentrations were determined by LC-MS/MS. Dox concentration measured from two cases was well within a concentration range considered therapeutic, whereas subtherapeutic dosing may have occurred in another two cases. There were two cases of fatal Dox ingestion, as well as a case of high dosage and advanced putrefaction, respectively. The liver concentration sum may be more useful if a fatal ingestion cannot be clearly separated from a person's medication usage. High concentrations could be observed in lung tissue, and combined concentrations of Dox and NDox may also be helpful in making a cause of death determination. There was a trend to a higher concentration sum in the brain with increasing combined levels in blood. Overall, the sum of the absolute figures allows a more accurate interpretation in Dox-related deaths as compared to the molar concentration ratio which may be helpful in acute ingestion. Determination of the N-desmethyl metabolite along with its parent is recommended and analysis should include more than a single specimen.