What causes ADHD?

By far, the most common cause of ADHD is a genetic proclivity (i.e., ADHD is often inherited). Studies suggest that the heritability rate of ADHD ranges from 0.75 to 0.91. The heritability rate indicates the percentage of ADHD in an individual resulting from genetic rather than environmental factors. Thus, a heritability rate of 0.75 means that 75% of the cause of ADHD is genetic.However, ADHD can also be caused or exacerbated by other factors, such as preterm birth, anemia, medications for asthma, and other environmental factors.