What is the main medication used as a mood stabilizer?

Lithium is considered the main medication used as a mood stabilizer, particularly in the treatment of bipolar disorder. Its effectiveness in stabilizing mood fluctuations and preventing both manic and depressive episodes is well-established through extensive clinical research. Lithium operates by affecting the neurotransmitter systems in the brain, contributing to the regulation of mood and emotional stability.

While valproate and lamotrigine are also utilized as mood stabilizers, especially in patients with bipolar disorder, they have distinct mechanisms of action and are generally considered auxiliary options alongside lithium. Valproate is primarily an anticonvulsant that has mood-stabilizing properties, and lamotrigine is often favored for the depressive episodes in bipolar disorder.

Sertraline, on the other hand, is classified as a selective serotonin reuptake inhibitor (SSRI) used primarily for the treatment of depression and anxiety disorders, rather than being a first-line mood stabilizer. Thus, in the context of mood stabilization, lithium stands out as the primary and most recognized agent, making it the correct answer.