Glutamate is the main excitatory
neurotransmitter in the central nervous system. Dysfunction of the glutamatergic system plays an important role in the pathogenesis of
schizophrenia. Therefore,
glutamatergic agents such as
N-methyl-D-aspartate receptor co-agonists (ie,
glycine, D-
cycloserine) and
glycine transporter type 1 inhibitors (eg,
sarcosine) are studied for their efficacy in ameliorating negative and cognitive symptomatology in patients with
schizophrenia. We report the case of a 23-year-old schizophrenic patient treated with
quetiapine and
citalopram, who was offered concomitant
sarcosine treatment. After obtaining an informed consent, we started administration of 2 g of
sarcosine per day to treat persistent negative and
cognitive symptoms. The patient's activity and mood improved within 2 weeks, but in the following 2 weeks the patient reported increased drive, activity, libido, unpleasant inner tension, and irritability. We ruled out
hypomania and decided to decrease the daily dose of
sarcosine to 1 g, which resulted in reduction of drive and irritability. Activity and mood improved compared with his state before adding
sarcosine. We suggest a
sarcosine dose between 1 g and 2 g per day with an initial dose of 2 g, but if side effects occur, the dose should be decreased to 1 g per day. We would like to emphasize the clinically important
glutamate-
serotonin interaction during concomitant use of
sarcosine,
citalopram, and
quetiapine in our patient, which may lead to serious discomfort.