There are three possible mechanisms responsible for impaired 5‐HT1A function in depression: social isolation reducing 5‐HT1 neurotransmission, 5‐HT2 receptors inhibiting 5‐HT1 neurotransmission, and hypercortisolaemia inhibiting 5‐HT1 neurotransmission.27 This evidence concerns the gene HTR2A and depressive symptom measurement.