Amitriptyline antidepressant tablets and their packaging. Amitriptyline belongs to the tricyclic antidepressant (TCA) class of drugs. It works by inhibiting the reuptake of the neurotransmitters serotonin and noradrenaline in the brain. TCAs can cause unpleasant side effects, including a dry mouth, drowsiness, irregular heartbeat and low blood pressure.