CYP2D6*81 is assigned no function based on limited evidence. CYP2D6*81 was identified in a subject demonstrating impaired enzyme activity based on experiencing adverse effects with venlafaxine and subsequently elevated nortriptyline levels (23799451). CYP2D6*81 is defined by an early stop codon yielding a truncated and nonfunctional protein. Therefore, consensus among experts was no function with an activity value of 0 based on limited evidence.