Effect of Estrogen Treatment on Drug Metabolism and Transport

January 7, 2026 updated by: Lauren Cirrincione, University of Washington

Effect of Gender-Affirming Estrogen Therapy on Drug Metabolism, Transport, and Gut Microbiota

This project will evaluate the effect of estrogen treatment on how other medications are processed by the body.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

Estradiol is prepared as a medication that patients may take to increase hormone levels. Changes in estradiol concentrations in the body may affect how the body processes other medicines. The purpose of this study is to find out how estradiol therapy affects a single tracer dose of approved medicines in the blood (midazolam, digoxin, and acetaminophen) and to confirm estradiol treatment does not affect natural bacterial in the gut.

Study Type

Interventional

Enrollment (Actual)

22

Phase

  • Phase 4

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • Washington
      • Seattle, Washington, United States, 98195
        • University of Washington

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years to 45 years (Adult)

Accepts Healthy Volunteers

Yes

Study Population

Transgender adults planning to take injectable estradiol or estradiol tablets for gender-affirming medical care.

Description

Inclusion Criteria:

  • Self-identified trans* adult 18-55 years of age.
  • Not taking estradiol treatment currently.
  • Planning to start injectable estradiol or estradiol tablets for gender-affirming medical care.

Exclusion Criteria:

  • Unwilling/unable to return for project follow-up visits.
  • Unwilling/unable to provide written informed consent.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Other
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: Healthy transgender adults
Healthy transgender adults will be studied on two separate study days and serve as their own control.
Drug: Midazolam oral solution
2 mg single-dose before and during estradiol treatment.
Drug: Digoxin Oral Tablet
0.25 mg single-dose before and during estradiol treatment.
Drug: Acetaminophen Oral Tablet
500 mg single-dose before and during estradiol treatment.
Drug: Midazolam Injectable Solution
1 mg intravenous single-dose before and during estradiol treatment.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
midazolam AUC ratio (treatment/control)
Time Frame: 0-6 hours
ratio of the area under of the plasma concentration time curve (AUC) of midazolam in the presence to absence of gender-affirming estradiol treatment.
0-6 hours
digoxin renal clearance (treatment/control)
Time Frame: 0-48
ratio of digoxin renal clearance in the presence to absence of gender-affirming estradiol treatment.
0-48

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
midazolam Cmax ratio (treatment/control)
Time Frame: 0-6 hours
ratio of the maximum plasma concentration (Cmax) of midazolam in the presence to absence of gender-affirming estradiol treatment
0-6 hours

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of Washington

Collaborators

National Institute of General Medical Sciences (NIGMS)

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

November 1, 2022

Primary Completion (Actual)

July 30, 2025

Study Completion (Actual)

July 30, 2025

Study Registration Dates

First Submitted

July 19, 2022

First Submitted That Met QC Criteria

July 19, 2022

First Posted (Actual)

July 21, 2022

Study Record Updates

Last Update Posted (Actual)

January 9, 2026

Last Update Submitted That Met QC Criteria

January 7, 2026

Last Verified

January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • STUDY00014091
  • 1K23GM147350 (U.S. NIH Grant/Contract)

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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