Lincoln was contemporaneously described as suffering from "melancholy," a condition which modern mental health professionals would characterize as clinical depression. Whether Lincoln may have suffered from depression as a genetic predilection, as a reaction to multiple emotional traumas in his life, or a combination thereof is the subject of much current conjecture.
What is clear is that Lincoln suffered particular bouts of depression after major events of his life such as the death of Ann Rutledge (Abraham Lincoln's first love ) in August of 1835, the cessation of Lincoln's engagement to Mary Todd Lincoln in January of 1841 (after which several close associates feared Lincoln's suicide), and after the Second Battle of Bull Run . It is also clear that Mary Lincoln felt her husband to be too trusting, and that his melancholy tended to strike at times that he was betrayed or unsupported by those he put faith in.
Lincoln would often combat his melancholic moods by delving into works of humor, likely a healthy coping mechanism for his depression.
As a treatment for his mental condition Lincoln took medication in the form of pills known as the "blue mass" , the active ingredient in which was elemental mercury – a substance now known to be a neurotoxin in its vaporic state. Whether mercury poisoning may have affected Lincoln's demeanor before or after he ceased its use in 1861 is unknown, but still remains the subject of conjecture by some historians. Lincoln himself took solace in the medication, if only as a placebo .