Methylphenidate, amphetamines, and atomoxetine have no inhibitory effects on the cytochrome P450 isoenzymes. The liver does not metabolize methylphenidate.
Amphetamines have multiple metabolic pathways, one of which is 2D6. Atomoxetine is a 2D6 substrate whose metabolism will be altered by 2D6 inhibitors/inducers. Guanfacine and clonidine are 3A4 substrates whose metabolism may change with 3A4 inducers or inhibitors. While pharmacokinetic drug interactions may be limited, pharmacodynamic interactions exist with psychiatric, medical, over-the-counter medications, and herbs/supplements/caffeine. While these drug interactions are too numerous to mention here, clinicians should be mindful of side effects that can arise. It is best to query patients about all prescriptions and over-the-counter drugs (including caffeine) before starting ADHD medication.
Complementary and alternative treatment options
In Australia, 50 families were surveyed regarding their use of complementary and alternative medicine (CAM) and 67.6% of families reported current or past CAM (Sinha and Efron, 2005). Of the 23 different therapies reported, the most common was modified diet (33 families), vitamins and/or minerals (16), dietary supplements (12), aromatherapy (12), and chiropractic manipulation (10). Of the families that participated in the survey, 64% reported that they informed the paediatrician of their CAM use and slightly more than half the families used CAM to avoid medication side effects. Such treatments include neurofeedback, homeopathy, acupuncture, restriction and elimination diets, megavitamins, chiropractic manipulation, omega fatty acids, sugar elimination, pycnogenol, St John’s wort, iron supplementation, and others. Clinicians need to assist patients and family in evaluating those treatments shown to be effective by research.