Mianserin HCl is the hydrochloride salt of mianserin, a tetracyclic antidepressant used primarily in the treatment of depression, especially for patients unresponsive to other antidepressants. It alleviates symptoms including low mood, anxiety, and sleep disturbances. Its sedative effects make it suitable for depression accompanied by insomnia or agitation. Off-label uses include certain anxiety disorders and chronic pain. The mechanism involves antagonism at serotonin (5-HT2A/2C), histamine H1, and alpha-adrenergic receptors, with alpha-2 autoreceptor blockade enhancing norepinephrine and serotonin release; it has minimal monoamine reuptake inhibition. Generally well-tolerated, it is often chosen for elderly patients or those with cardiovascular issues. As a research reagent, it is supplied at ≥98% purity for pharmaceutical and biochemical studies.