The active substance in Zypadhera, olanzapine, is an antipsychotic medicine. It is known as an ?atypical? antipsychotic because it is different from the older antipsychotic medicines that have been available since the 1950s. Olanzapine attaches to several different receptors on the surface of nerve cells in the brain. This disrupts signals transmitted between brain cells by ?neurotransmitters?, chemicals that allow nerve cells to communicate with each other. It is thought that olanzapine?s beneficial effect is due to it blocking receptors for the neurotransmitters 5-hydroxytrypamine (also called serotonin) and dopamine. Since these neurotransmitters are involved in schizophrenia, olanzapine helps to normalise the activity of the brain, reducing the symptoms of the disease. Olanzapine has been authorised in the European Union (EU) since 1996. It is available as tablets, orodispersible tablets (tablets that dissolve in the mouth) and rapidly acting injections in Zyprexa, Zyprexa Velotab and other medicines. The olanzapine in Zypadhera is presented as a ?pamoate? salt, which makes the olanzapine less soluble. As a result, the active substance is released slowly for more than four weeks after injection of Zypadhera.