This is a 12-week clinical trial evaluating the efficacy and safety of memantine hydrochloride (Memantine HC1, brand name Namenda) in the treatment of executive function deficits (EFDs) in adults with Attention Deficit Hyperactivity Disorder (ADHD). After screening procedures, memantine is prescribed in randomized, double-blind fashion (equal chance of medication or placebo) for 12 weeks.

The investigators hypothesize that memantine hydrochloride will prove to be an effective, safe, and well-tolerated agent for the treatment of EFDs in individuals with ADHD interested in non-stimulant medications.

Inclusion Criteria:

1. Male and female adults ages 18-45 years;
2. a diagnosis of DSM-IV [78] ADHD-combined type
3. a score of at least 20 on the AISRS (a score of 20 in the AISRS identifies subjects with at least moderate severity of symptoms);
4. a BRIEF-A Global Executive Composite T-score of >6; and
5. proficiency in English. -

Exclusion Criteria:

1) Pregnant or nursing females; 2) investigator and his/her immediate family (spouse, parent, child, grandparent, or grandchild); 3) any serious, unstable medical illness including hepatic, renal, gastroenterological, respiratory, cardiovascular (including ischemic heart disease and hypertension), endocrinologic, neurologic, immunologic, or hematologic disease; 4) hypersensitivity to memantine; 5) multiple adverse drug reactions; 6) current or past history of seizures; 7) any history of a major psychiatric disorder including schizophrenia, psychosis, bipolar disorder (BPD), or autism spectrum disorder (ASD); 8) meets DSM-IV criteria in the last month for major depression or any major anxiety disorder or has a Hamilton Rating Scale for Anxiety (HAM-A) or Hamilton Rating Scale for Depression (HAM-D) score greater than 14; 9) meets DSM-IV criteria for substance abuse or dependence in the last month or has a positive drug urine screen; 10) judged to be at serious suicidal risk; 11) use of any other concomitant medication with primarily central nervous system activity; or 12) IQ < 80.

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