From the FDA Drug Label
Oral Administration, Monotherapy — Olanzapine is well absorbed and reaches peak concentrations in approximately 6 hours following an oral dose. Intramuscular Administration — ZYPREXA IntraMuscular results in rapid absorption with peak plasma concentrations occurring within 15 to 45 minutes
The onset of Zyprexa (olanzapine) is as follows:
- Oral administration: reaches peak concentrations in approximately 6 hours
- Intramuscular administration: reaches peak plasma concentrations within 15 to 45 minutes 1
From the Research
Zyprexa (olanzapine) typically begins to show initial effects within 1 week of starting treatment, with a statistically significant effect observed at week 1, and the effect increasing until week 3, after which it levels off. The onset of action varies depending on the condition being treated, with acute psychosis or mania potentially responding faster than chronic schizophrenia or bipolar disorder maintenance therapy.
Key Points
- Starting doses are usually 5-10 mg daily for adults, with gradual titration based on response and tolerability 2.
- Side effects like sedation and dizziness may appear early in treatment, while metabolic effects such as weight gain and increased blood glucose develop more gradually over weeks to months.
- Regular monitoring of weight, blood glucose, and lipids is important throughout treatment.
- Patients should be advised that while some symptom improvement may occur quickly, they should continue taking the medication as prescribed even if they feel better, as premature discontinuation can lead to symptom recurrence.
Evidence Summary
The most recent and highest quality study, a systematic review and meta-analysis published in 2022, found that olanzapine has a rapid onset of action, with a statistically significant effect observed at week 1, and the effect increasing until week 3, after which it levels off 2. This study included 35 randomized, placebo-controlled trials in adults with schizophrenia, and estimated the time to onset of action and time to maximum antipsychotic effect of olanzapine and other second-generation antipsychotics.
Clinical Implications
The findings of this study have important implications for clinical practice, as they suggest that olanzapine can provide rapid relief from symptoms of schizophrenia and other conditions, and that patients may be able to experience significant improvement in their symptoms within a few weeks of starting treatment. However, it is also important to note that the study found that the effect of olanzapine levels off after week 3, highlighting the importance of ongoing treatment and monitoring to maintain therapeutic benefits.