The pineal gland is not directly used as a treatment for Seasonal Affective Disorder (SAD); however, its secreted hormone, melatonin, plays a key role in the regulation of circadian rhythms and has been the focus of scientific investigation in SAD. The pineal gland synthesizes and releases melatonin in response to darkness, helping regulate sleep-wake cycles. In SAD, shorter daylight hours during winter are thought to disrupt normal circadian rhythms, possibly due to altered melatonin production or secretion timing.

Several studies have shown that melatonin levels and rhythms are often altered in individuals with SAD, supporting the hypothesis that the pineal gland's function is implicated in the disorder. More importantly, light therapy—a mainstay of SAD treatment—acts in part by suppressing melatonin secretion, thereby realigning circadian rhythms. Some controlled trials have also explored the use of melatonin supplementation or timed melatonin administration to improve circadian alignment in SAD patients, with modest efficacy reported when properly timed.

While the pineal gland itself is not a direct therapeutic target, its physiological functions form the basis for scientifically validated interventions in SAD. Thus, there is a strong scientific foundation for the involvement of the pineal gland (via melatonin and circadian regulation) in both the pathophysiology and treatment strategies for Seasonal Affective Disorder.