Is it true that people with adhd have slower reflexes?

Maybe. : Some add people are clutzes, others are very athletic. Reflex ability is complex so if someone is inattentive to their environment or over focused on the wrong item in the environment, then they may not respond quickly (reflexly) to an event. The deep tendon reflexes in add pts are usually more brisk than normals. A significant number if athletes have add.

Unlikely: I've not seen any studies that would indicate that and a brief journal search didn't turn up anything.

No evidence: I have never seen evidence that this is a characteristic of ADHD. ADHDers may need longer time is tests and such, but not on the basketball court or on the ball field. This does not relate to automobile accidents though, where ADHD teens have more accidents. This is not because they are slower to react, but more distracted while they drive, thus causing a DELAYED reaction.

No: people with ADHD have a normal range of reflexes.