Estradiol Topical and Clozapine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Clozapine
Estradiol Topical
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased clozapine exposure and increased risk of adverse effects
Interaction Deep Dive
Concomitant use of clozapine and CYP1A2 inhibitors (including combination oral contraceptives [COCs]) can increase clozapine exposure and increase risk of adverse reactions12. Concurrent use or discontinuation of COCs with clozapine could lead to clozapine toxicity or withdrawal psychosis, respectively. Additionally, cyclical worsening of psychosis during the COC-free interval each month has been reported 3. Before initiating clozapine, consider use of alternative contraception methods in patients taking COCs. If concomitant use is required, titrate clozapine very slowly (eg, start at 12.5 mg/day; if tolerated, target 50 mg/day at day 7, 100 mg/day at day 14, and 150 mg/day at day 21). Consider therapeutic drug monitoring (TDM) when starting or discontinuing COCs and adjust clozapine dosage as needed. If TDM is not available, consider decreasing clozapine dosage by half if COCs are initiated and monitor for clozapine adverse events; if COCs are discontinued, consider doubling dosage and monitor for decreased efficacy 4.
Why it happens (mechanism)
Inhibition of CYP1A2-mediated metabolism of clozapine; possible inhibition of CYP2C19- and CYP3A4-mediated metabolism of clozapine
Literature reports
3 reports — tap to read
a) Initiation of clozapine in a 17-year-old patient with schizophrenia receiving a combination oral contraceptive (COC) was associated with poor clozapine tolerability leading to discontinuation in a case report. She was receiving a COC (levonorgestrel 0.1 mg/ethinyl estradiol 20 mcg daily), melatonin (3 mg at bedtime), and polyethylene glycol 17 g as needed for constipation and was a nonsmoker. Pharmacogenomic testing determined she was a CYP1A2 and CYP2C19 rapid metabolizer, CYP2D6 normal metabolizer, CYP3A4 intermediate to normal metabolizer, and CYP3A5 poor metabolizer. Clozapine was titrated slowly (eg, starting at 12.5 mg/day and increased by 25 mg/day about every 4 days) due to the potential drug interaction with COCs. When the clozapine dose reached 150 mg after about 4 weeks, she had developed fatigue, worsening constipation, and increased appetite (with about 5 kg of weight gain). Clozapine was decreased to 100 mg/day over weeks 4 to 8; however, clozapine was eventually tapered and transitioned to an alternative treatment due to ongoing intolerance and limited efficacy for psychiatric symptoms. The elevated clozapine level was suspected to be due to the interaction between clozapine and COCs, which is primarily mediated via CYP1A2; her CYP1A2 and CYP2C19 rapid metabolizer phenotype did not seemingly mitigate the interaction 5.
b) Cyclical worsening of psychosis for about 1 week each month was reported in a 30-year-old female patient with treatment-resistant schizophrenia receiving chronic clozapine (350 mg/day) treatment and a combination oral contraceptive (COC). She was receiving the COC (drospirenone 3 mg/ethinyl estradiol 0.03 mg) for polycystic ovarian syndrome; additional significant medical history included hirsutism (treated with flutamide 750 mg) and obesity, and she was a nonsmoker. Her corrected-dose clozapine levels were 5.38 and 3.32 when on and off COC, respectively, and estimated dose-correction factor was 1.62. It was discovered that worsening of psychosis symptoms occurred during the combination oral contraceptive (COC)-free interval each month and improved within a few days after COC-free interval. Therefore, it is likely that the relative reduction in clozapine concentration during the COC-free interval contributed to worsening of psychosis. Aripiprazole (titrated to 40 mg/day) and trihexylphenidyl (2 mg/day) were added and cyclical worsening of symptoms stopped 3.
c) A 33-year-old female patient with chronic schizophrenia experienced elevated clozapine levels and potential clozapine-induced adverse effects including fever (without infection) and constipation when clozapine was coadministered with a combination oral contraceptive (COC). Her medications included only clozapine (starting with 50 mg/day and uptitrated to 300 mg/day) and a COC (norethindrone 0.5 mg/ethinyl estradiol 0.035 mg). She smoked 1 pack/day. Her corrected-dose (C/D) clozapine levels were 3.34 and 1.5 when on and off COC, respectively, and estimated dose-correction factor was 0.55. Additionally, 3 previous case reports demonstrated inhibition of clozapine metabolism with COCs (all including ethinyl estradiol with or without norethindrone or levonorgestrel). The drug interaction was determined to be clinically relevant in case 1 by resolution of potential clozapine-induced adverse events (ie, drowsiness, weakness and dizziness) after COC discontinuation, in case 2 by addition of COC causing potential clozapine-induced adverse events (ie, drowsiness, anergy, dizziness and orthostatic hypotension) followed by noticeable improvement after COC discontinuation, and in case 3 because discontinuation of COC caused clozapine to be ineffective and psychotic relapse occurred. Using combined data, the mean dose-correction factor for the 4 cases was 0.47 (range, 0.39 to 0.51). This study demonstrated that significant changes in clozapine therapeutic drug monitoring results can occur with the addition or discontinuation of COCs with estrogens in patients receiving clozapine 4.
Common questions
Can I take Estradiol Topical and Clozapine together?
Increased clozapine exposure and increased risk of adverse effects Always confirm with your pharmacist or prescriber before making any change.
How serious is the Estradiol Topical and Clozapine interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Estradiol Topical or Clozapine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (5)
- Product Information: CLOZARIL(R) oral tablets, clozapine oral tablets. HLS Therapeutics USA Inc (per FDA), Rosemont, PA, 2025. DailyMed
- Product Information: VERSACLOZ(R) oral suspension, clozapine oral suspension. TruPharma LLC (per FDA), Tampa, FL, 2025. DailyMed
- Suhas S, Manchegowda S, Venkatasubramanian G, et al: Clozapine and oral contraceptives-implications beyond pharmacokinetics: a case report. J Clin Psychopharmacol 2021; 41(4):487-490. PubMed
- Schoretsanitis G, Kane JM, & de Leon J: Adding oral contraceptives to clozapine may require halving the clozapine dose: a new case and a literature review. J Clin Psychopharmacol 2020; 40(3):308-310. DOI
- Kuhn AK, Determan ML, Wright JA, et al: The potential influence of estrogen-containing oral contraception on clozapine metabolism in a patient with known pharmacogenomic status. Ment Health Clin 2024; 14(3):220-223. PubMed
Keep reading about Clozapine
Keep reading about Estradiol Topical
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