In his stand-up and best-loved comedies, including Aladdin and Mrs. Doubtfire, Robin Williams was known for his rapid-fire impersonations and intensely playful energy. His most critically acclaimed work, however, including his Oscar-winning turn in Good Will Hunting, married humor with sharp introspection and appreciation for melancholy.



Reports of his death from apparent suicide on August 11 at the age of 63 have prompted much speculation about the actor’s personality and mental health. Williams had been seeking treatment for severe depression, and many commenters have labeled that as the reason for his death. Whereas the majority of people who commit suicide suffer from depression, less than 4 percent of those eventually take their lives.



Clearly, more factors are at work as causes of suicide than depression alone. The severity of mood disorders, past suicide attempts and substance abuse are all thought to increase the risk. Recent evidence also suggests that the mixed-depressive form of bipolar disorder can be a particularly dangerous time that can often go undetected or masquerade as general depression and irritability.



In 2006 Williams told interviewer Terry Gross on the radio show Fresh Air that he had experienced depressive episodes, but said that he had not been diagnosed with clinical depression or bipolar disorder—an illness typified by extreme emotional highs and lows, where people alternate between states of manic energy and deep depression. He also discussed his struggles with addiction and substance abuse—cocaine in the 1970s, and later, alcohol, for which he entered treatment in 2006. "Do I perform sometimes in a manic style? Yes," Williams said. "Am I manic all the time? No. Do I get sad? Oh yeah. Does it hit me hard? Oh yeah," he said at the time.



Depression, which affects about 16 million people in the U.S. according to the National Institutes of Mental Health, and more than 350 million globally according to the World Health Organization, is thought to be the result of interacting social, biological and environmental factors. The word “depression” is tossed around casually, but in reality the condition can be quite debilitating. People with major depressive disorder (also known as clinical, major or unipolar depression) exist beyond the realm of sadness. In fact, they can feel numb to the world and often become lethargic and lose interest in people and activities that formerly brought them joy. When the disorder is at its most severe, people with depression may even experience psychosis—seeing or hearing things that aren’t there.



Unsurprisingly, the more severe the depression symptoms the more likely the person is at risk for suicide. Mild to moderate depression or dysthymia—chronic gloominess that is less serious than major depression—is not considered a risk factor for suicide. When left untreated, however, moderate depression can turn severe over time as the episodes build on one another.



Although women attempt suicide more often, men are more likely to complete the act. That morbid fact is frequently attributed to the method: Men use firearms or hanging—much harder to recover from than overdosing on pills, women’s method of choice. Yet men are also more likely to be depressed for a longer period of time and to have their depression go undetected than are women.



The longstanding biological explanation of depression—that people with the disorder have low levels of the neurotransmitter serotonin—is now considered overly simplistic. But serotonin, which facilitates learning and memory, is thought to be involved in some capacity; people with depression struggle to break negative, recursive thought patterns that inhibit their ability to learn from new information. In a 2014 study, John Keilp, a neuropsychologist at Columbia University, and colleagues found that people with depression who attempt suicide tend to have shorter attention spans and worse memory capacity than those with the disorder who do not attempt suicide.



Cognitive behavioral therapy and medication can work together to correct those counterproductive thought patterns, but that type of recovery becomes more difficult when mind-altering recreational substances are added to the equation. This challenge is particularly true with the introduction of sedatives, or “downers,” such as benzodiazepines and alcohol. Alcohol depresses the brain’s reward centers even further, making it harder bounce back. Approximately 60 percent of people who commit suicide have consumed alcohol at the time of death.



Another condition that may appear as depression but is actually a facet of bipolar disorder, called a mixed-depressive episode, can also elevate the risk for suicide. This condition is characterized by a depressive episode with three or more “hypomanic” symptoms—which can include irritability, distractibility and agitation. Mixed episodes combine the racing thoughts of a manic episode, but with a distinctly negative instead of euphoric tinge Mixed states in turn may deepen depression and make it more resistant to treatment. A 2013 review in The American Journal of Psychiatry suggests that suicidal ideation and past suicide attempts are more frequent in people during mixed-depressive episodes compared with those experiencing depression alone.



This summer Williams reportedly entered Hazelden, an addiction treatment center in Minnesota. He had not fallen off the wagon, but was taking the opportunity to “fine-tune and focus on his continued commitment to [sobriety].” Although it was not enough in the end—the effects of addiction can linger for years after substance abuse has stopped, and depression is a supremely intractable disorder— hopefully the bravery he displayed in addressing his problems head-on will encourage more people seek help before it's too late.



A number of other factors can contribute to suicide risk—poverty, for one, family history of suicide, for another. But the tragedy of Williams’s death should remind us that the most debilitating and life-threatening mood disorders can strike anyone, and once they do, it can be awfully hard to find release.



For more on suicide, read our special report: "Suicide: Genius, Suicide and Mental Illness: Insights into a Deep Connection"