Doctors, psychologists, and historians have speculated as to Wolfgang Amadeus Mozart’s physical and mental state for over two centuries. His death in 1791 at the age of 35 has always been a mystery, and the 1984 film Amadeus brought more attention to the theory that he was poisoned by a rival. His death having been a homicide is unlikely, and over the years 140 different illnesses have been suggested as his true cause of death. Since we cannot go back 200 years and do an autopsy, this will probably always remain a mystery.
Aside from all those physical diagnoses, 27 different mental illnesses have also been suggested as explanations of Mozart’s unusual behavior. It is possible he would not have qualified for any mental diagnosis that we know of today, or that he had a combination of diagnoses, as comorbidity - a person qualifying for multiple diagnoses - is quite common. In fact, around half of those who qualify for one psychiatric diagnosis are found to meet criteria for a second diagnosis.
The one diagnosis which can be most plainly observed in the last year of Mozart’s life is major depression. In his letters he described having "black thoughts", difficulty concentrating, and a lack of energy. He also describes feeling tearful, less creatively inclined than in the past, and guilty. All of these things meet the criteria for a modern diagnosis, but this is just the final year of his life. We still don’t have explanations for the previous years.
Variations of bipolar disorder have been observed and diagnosed in other creative geniuses. It is characterized by a fluctuation between depressive episodes and manic or hypomanic episodes. We already know he was in a depressive episode leading up to his death, but there is not very much evidence of such episodes earlier in his life. There is, however, some evidence of hypomanic episodes, as seen in his impulsivity, difficulty with finances, and behavior on his most productive days. He often woke up at 6am and worked until 2am the following morning. Combined surges of energy and creativity are common in manic or hypomanic episodes, though in Mozart’s case they only lasted long enough to meet the criteria for a mild form of bipolar disorder called cyclothymia.
Mozart was described by several people who knew him as having tics like those observed in Tourette’s Syndrome - repetitive movements, jumping, facial grimaces - though these can also be explained by ADHD or autism. Also attributable to those diagnoses is his habit of making inappropriate jokes and his coprographia. Not to be confused with coprophagia (eating feces), coprographia is the frequent use of scatological language. Whether this was because of a diagnosable mental disorder or poor manners we do not know, though it is worth noting that another creative genius - Shakespeare - reportedly used similarly crude language. One trait of Mozart’s which could be a sign of autism is his sensitivity to loud sounds, which could make him physically ill. This is also easily explained by the fact that he was a musical genius, so he likely had a unique relationship with auditory input.
Finally, personality disorders have been suggested as possible diagnoses for the Wunderkind. His reliance on others, aversion to being alone, and constant need for reassurance that people did care about him all point to Dependent Personality Disorder. His impulsivity, problems with money, temper outbursts, and highly reactive mood swings indicate Borderline Personality Disorder.
Of course, this can be framed as a case of nature vs nurture. His upbringing was unusual, even by today’s standards, which can explain some of his behavior in adulthood. From the age of six, instead of being sent to school like other children, Mozart was taken around Europe to perform with his sister. The tour lasted over three years. He achieved celebrity at a young age but as a result was not educated or socialized as well as his peers. His musical career was the focus of the entire family, as it was a significant source of income, so he would have been under enormous pressure throughout his childhood and adolescence. His behavior later in life is described as very childish, like the regression seen in children who had to grow up too quickly. In the modern world he may have ended up like those child stars who act out and get in trouble as soon as they’re legally independent.