People swear by essential oils for everything, so it should come as no surprise that there are several that are thought to improve symptoms of ADHD. Personally, I've noticed a difference in my ability to concentrate, energy and stress levels, mental clarity, and mood when I diffuse essential oils like orange, bergamot, frankincense, and clary sage.
A USB desktop diffuser, like the BBSKIN Mini Kids USB Essential Oil Diffuser ($15), serves as a visual reminder to actually use the diffuser every day when I sit down at my desk to work (there's that object permanence again).
Other scents that may benefit people with ADHD include vetiver and rosemary. A study in the Journal of Intercultural Ethnopharmacology concluded that vetiver essential oil may improve alertness and task performance." Similarly, a study published in Therapeutic Advances in Psychopharmacology found that rosemary had a positive effect on cognitive performance.