I tried Memantine(Namenda) 10-20mg years ago to reduce tolerance to opioid pain killers I was on at the time. I can't say I recall any side effects. I know that your child is using it for a completely different purpose though. From a quick glance on google, reading several articles, Memantine when used on its own showed no significant difference from placebo but when used to augment other meds it helped improve language development and social behavior in children with autism. Memantine is a weird medication that has a lot of off label uses that seem completely unrelated to one another, anything from treating to OCD to being used to slow the progress of Alzheimers. I seem the recall the main side effect from others that I knew that used it was brain fog, maybe some dizziness, that went away in a couple weeks once the body got used to the drug.
Quote:
Autism and Pervasive Developmental Disorder Not Otherwise Specified are common developmental problems often seen by child neurologists. There are currently no cures for these lifelong and socially impairing conditions that affect core domains of human behavior such as language, social interaction, and social awareness. The etiology may be multifactorial and may include autoimmune, genetic, neuroanatomic, and possibly excessive glutaminergic mechanisms. Because memantine is a moderate affinity antagonist of the N-methylD-aspartic acid (NMDA) glutamate receptor, this drug was hypothesized to potentially modulate learning, block excessive glutamate effects that can include neuroinflammatory activity, and influence neuroglial activity in autism and Pervasive Developmental Disorder Not Otherwise Specified. Open-label add-on therapy was offered to 151 patients with prior diagnoses of autism or Pervasive Developmental Disorder Not Otherwise Specified over a 21-month period. To generate a clinician-derived Clinical Global Impression Improvement score for language, behavior, and self-stimulatory behaviors, the primary author observed the subjects and questioned their caretakers within 4 to 8 weeks of the initiation of therapy. Chronic maintenance therapy with the drug was continued if there were no negative side effects. Results showed significant improvements in open-label use for language function, social behavior, and self-stimulatory behaviors, although self-stimulatory behaviors comparatively improved to a lesser degree. Chronic use so far appears to have no serious side effects.
http://www.ncbi.nlm.nih.gov/pubmed/17690064