The introduction of long-acting injectable atypical antipsychotics has ensured adherence to treatment in patients with low awareness of the disorder, with an acceptable rate of side effects. In the case of long acting olanzapine injection in particular, has particular relevance the existence of a special side-effect called post-injection syndrome. This rare side effect consisting in the presence of symptoms of olanzapine overdose after intramuscular administration of medication has led to restrictions on the use of the drug and the need for patient observation for three hours after each injection. We report a case of postinjection syndrome, to our knowledge, the first in Spain since the commercialization of Zypadhera. As in most cases described in the literature have symptoms of overdosage of olanzapine (dysarthria, sedation, fatigue, etc.) that are selflimiting without any therapeutic measure and are accompanied by supratherapeutic plasma levels of olanzapine.