Why is adhd/add more common in boys than girls?

The Why Questions: The why questions in medicine are often unanswerable. They just are the way they are in nature. These types of questions can be discussed and debated by the best minds in medicine, but there is little to come of such a debate since it will not change the realities on the ground in the lives of patients.

Nobody knows: Twice as many boys than girls are diagnosed with add. Girls are more likely to present with inattentiveness rather than hyperactivity. In adults the ratio of men to women with add is 1.6. The reasons for the different prevalence is unknown, and is being investigated.

Not quite: Add is more common in girls than in boys, 75% girls, 25% boys. Adhd is more common in boys than girls. The reason is likely genetic, but could involve multiple genes or be multifactorial.

Brain Development: Nobody really knows but some experts suggest that based upon how the brain develops in boys different than girls may have something to do with it. 1 out 4 boys is now diagnosed with ADHD. The way public education has become more geared towards girls also has been suggested. An interesting book to read is Dr Sax's book "Boys Adrift". You may find your answer there.