While we don’t know the exact cause of OCD or ADHD, physically, we do have research that describes correlations. Particularly for ADHD, we know certain areas of the brain that control executive function are generally smaller in people with ADHD. We also know that they generally have lower levels of certain brain chemicals, and we have learned far more about it through radioactive isotope examination of the brain as well.

For OCD: Research suggests that OCD involves problems in communication between the front part of the brain and deeper structures of the brain. These brain structures use a neurotransmitter (basically, a chemical messenger) called serotonin. Pictures of the brain at work also show that, in some people, the brain circuits involved in OCD become more normal with either medications that affect serotonin levels (serotonin reuptake inhibitors, or SRIs) or cognitive behavior therapy (CBT).

Just because we don’t know the precise cause doesn’t mean we cannot, in the meantime, help alleviate the symptoms for someone suffering from the syndrome (since we don’t know the precise cause).

Please don’t get in the way of this by implying people are “making it up,” because, simply, they are not. Both of these are extremely well studied syndromes, but really only in the last few decades.