Methylphenidate is a norepinephrine and dopamine reuptake inhibitor, which means that it increases the level of the dopamine neurotransmitter in the brain by partially blocking the dopamine transporter (DAT) that removes dopamine from the synapses. Animal studies using rats with ADHD-like behaviours were used to assess the safety of methylphenidate on the developing brain and found that psychomotor impairments, structural and functional parameters of the dopaminergic system were improved with treatment. It cannot cross the blood-brain barrier, but is converted by the body into L-Dopa, which can. Tyrosine must be taken on an empty stomach and the dosages recommended by most supplement companies may not be sufficient for a noticeable effect. People with ADHD more often have difficulties with social skills, such as social interaction and forming and maintaining friendships. About half of children and adolescents with ADHD experience social rejection by their peers compared to 10–15% of non-ADHD children and adolescents. Abnormal distal sudomotor findings are frequently reported suggesting patchy small fiber neuropathy in a large subset of POTS patients. The finding of abnormal quantitive sudomotor axon test results or skin biopsies in this subset have been interpreted as supporting an autonomic neuropathic process.
