4. Smoking
About 40 percent of those with adult ADHD smoke, compared with about 26 percent of the general population. In many ways, this makes sense, since smoking is often used by some as “something to do,” an activity to keep the hands busy. There’s also the effect that nicotine has on ADHD, which may help alleviate some symptoms. Those suffering from ADHD are also more likely to have problems with alcohol or drug addiction.