Even if we leave out combat deaths and injuries, civilian casualties, property damage, rape and pillage, lingering danger of unexploded munitions, economic disruption, refugees, famine and disease, and possible destruction of the planet, we're still left with things like increased drug addiction. At the beginning of the 19th century drug addiction was rare in the English-speaking world, but at the end of the century it was common, at least in the United States. By a conservative estimate the U.S. had 200,000 addicts in 1900, with most of the increase coming in the late 1800s.
Some historians think the war's influence has been exaggerated.
A major factor in the rise of drug use no doubt was the simple fact that more stuff became available as scientists explored the wonders of drug chemistry. Morphine, for example, was first synthesized in 1803, cocaine in 1859. Still, even allowing for some exaggeration on the part of historians, you have to think the Civil War had some impact. Narcotics were handed out like candy by army surgeons, who were surrounded by suffering and had few remedies to offer other than painkillers. Opiates were used to treat not just wounds but chronic campaign diseases such as diarrhea, dysentery, and malaria.