Final answer:
Tricyclic antidepressants are used primarily to treat major depression by inhibiting the reuptake of serotonin and norepinephrine, which increases their levels in the brain and can improve mood. They are not to be used on an "as-needed" basis and may have side effects, although compared to SSRIs, tricyclic antidepressants can offer a modest increase in efficacy with slightly milder side effects.
Step-by-step explanation:
Tricyclic antidepressants, such as imipramine and amitriptyline, are a class of medications widely used to treat major depression. Despite some structural similarities to phenothiazines, tricyclic compounds are chemically distinct due to features like the unconjugated ethylene group in imipramine's middle ring. The primary therapeutic action of tricyclic antidepressants involves inhibiting the reuptake of both serotonin and norepinephrine, leading to increased levels of these neurotransmitters in the synaptic cleft.
It is worth noting that administration of tricyclic antidepressants to non-depressed individuals can result in unpleasant effects such as sleepiness, light-headedness, and increased anxiety; however, when given to patients with depression over a period of several weeks, an improved mood is often observed. This denotes that such medications are not intended for "as-needed" use but require continuous administration to achieve the beneficial antidepressant effects. Compared to selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants may exhibit a modest increase in efficacy and have slightly milder side effects.
Due to their ability to increase neurotransmitter levels, antidepressants are a key treatment option for depression and are often complemented by other forms of therapy. The enhanced neurotransmitter activity in the CNS, specifically involving serotonin, plays a crucial role in mood regulation and the treatment of various psychiatric disorders.