Used primarily in pharmaceutical research as a major active metabolite of the antidepressant venlafaxine. Plays a key role in the therapeutic effects of the parent drug by inhibiting the reuptake of serotonin and norepinephrine in the central nervous system. Commonly analyzed in metabolic studies and drug monitoring to assess patient compliance, metabolic activity, and pharmacokinetic profiles. Also utilized in the development and validation of analytical methods for detecting antidepressants in biological samples.