Definitely drug/alcohol. Among adults who have an alcohol use disorder, ADHD is 5-10 times more common (American Addiction Centers); Among children, children with ADHD are 2-3X more likely to abuse substances than kids in the general population. Other areas where folks with ADHD have pretty alarming stats: School (46% more expulsions), Healthcare (33% more ER visits, 3x more motor vehicle accidents), Home (3-5x more divorce). It's a really important problem that has far reaching impacts, where multiple solutions are necessary to make a sustained dent to improve the lives of people with ADHD!
The ADHD community, like many underserved populations, tends to be overrepresented in the prison population due to lack of accommodations and resources, along with stigma. There's a great deal of peer-reviewed research on the subject of ADHD and drug addiction. The overall gist is that people with ADHD are at higher risk for substance use disorders than their neurotypical counterparts due to several possible factors, including chronically low levels of dopamine and contextual factors like lack of resources and stigma.
Keep in mind that those numbers may be skewed based on how ADHD was diagnosed in the past. Only in the last few years have we started to see more traditionally "successful" people being diagnosed with ADHD, which is revealing that the percentage of the general population with ADHD is likely much higher than previously thought. ADHD was considered a "disease" that caused people to make trouble. That created a vicious cycle of stigma and punishment for those who had been diagnosed or expressed obvious symptoms. Meanwhile, lots of people with more subtle ADHD symptoms, stronger support systems, and greater privilege were never diagnosed at all. I'd take that 27% statistic with a big grain of salt, especially if it's coming from nootropics websites.
When I started my research on my own ADHD condition and nootropics I found out that 27% of the USA jail population has ADHD.
Curious about other stats about ADHD in other populations, for example how much of the drug abuse population has ADHD for example.
Curious about what you might have found upon such areas of inquiry..