Concomitant amlodipine use was associated with lower serum olanzapine concentrations and smaller improvements in selected clinical domains, suggesting that closer monitoring of clinical response and serum olanzapine concentrations may be considered when amlodipine is co-prescribed.
Key Findings
Results
Mean serum olanzapine concentration was significantly lower in patients receiving olanzapine plus amlodipine compared to those receiving olanzapine alone.
Combination group mean serum olanzapine concentration: 40.56 ± 18.86 ng/mL
Olanzapine-alone group mean serum olanzapine concentration: 50.23 ± 23.41 ng/mL
Unadjusted p = 0.027; age-adjusted p = 0.032
Both groups received olanzapine 10 mg/day; experimental group also received amlodipine 5 mg/day
Study included 45 patients in the experimental group and 52 in the control group
Results
Improvements in positive symptoms, negative symptoms, and SDSS scores were smaller in the combination (olanzapine plus amlodipine) group compared to the olanzapine-alone group.
PANSS and SDSS scores were assessed at baseline and week 7
Adverse events were evaluated at week 9
PANSS total scores and general psychopathology changes did not differ significantly between groups
Serum olanzapine concentration was not significantly correlated with any PANSS or SDSS change at the individual level.
Individual-level analyses did not establish a concentration-response relationship
This finding limits the ability to attribute clinical outcome differences directly to the lower drug concentrations observed in the combination group
The retrospective design precludes causal inference
Results
Recorded adverse-event rates did not differ significantly between the combination group and the olanzapine-alone group.
Adverse events were recorded and evaluated at week 9
No statistically significant difference in adverse-event rates was found between groups
Haemodynamic safety could not be fully evaluated because complete standardised blood-pressure data were unavailable
Methods
The study was a retrospective design including inpatients with both schizophrenia and hypertension, which limits causal inference.
Retrospective study design
Experimental group: 45 inpatients with schizophrenia and hypertension receiving olanzapine 10 mg/day plus amlodipine 5 mg/day
Control group: 52 inpatients with schizophrenia receiving olanzapine 10 mg/day alone
Haemodynamic safety could not be evaluated due to unavailability of complete standardised blood-pressure data
Age adjustment was applied in the primary concentration analysis (age-adjusted p = 0.032)
What This Means
This research examined whether taking amlodipine (a common blood pressure medication) at the same time as olanzapine (an antipsychotic medication used to treat schizophrenia) affected how much olanzapine was present in patients' blood and how well the treatment worked. The study looked at hospital records from 97 patients with schizophrenia, comparing those who took both medications to those who took olanzapine alone. Researchers found that patients taking both medications had notably lower levels of olanzapine in their blood — about 40 ng/mL on average compared to about 50 ng/mL in the olanzapine-only group — even though everyone was taking the same dose of olanzapine.
The study also found that patients on the combination of both drugs showed smaller improvements in certain symptom areas, specifically positive symptoms (like hallucinations), negative symptoms (like social withdrawal), and social functioning scores, over a 7-week period. However, overall symptom scores and general psychopathology scores did not differ between the two groups. Importantly, when looking at individuals, lower olanzapine blood levels did not consistently predict worse outcomes, so it remains unclear whether the lower drug levels directly caused the smaller improvements. Rates of recorded side effects were similar between the two groups.
This research suggests that when amlodipine and olanzapine are prescribed together — a common situation since many people with schizophrenia also have high blood pressure — doctors may want to more closely monitor both blood olanzapine levels and how well patients are responding to treatment, especially if a patient does not seem to be improving as expected. Because this was a retrospective study (looking back at existing records rather than running a controlled experiment), it cannot definitively prove that amlodipine causes lower olanzapine levels or worse outcomes, and further prospective research would be needed to confirm these findings.
Chen X, Ma J, Xuan X, Huang M, Yang X, Huang B. (2026). Association of Concomitant Amlodipine Use With Serum Olanzapine Concentrations and Clinical Outcomes in Patients With Schizophrenia.. Human psychopharmacology. https://doi.org/10.1002/hup.70062