Impact of Oral vs. Transdermal Oestrogen on Cortisol & CBG Before SST - NCT07928024

Cortisol is a hormone that helps the body handle stress and maintain blood pressure. Doctors check if the adrenal glands (which make cortisol) are working correctly using a Synacthen test (SST). This test involves giving a drug that stimulates cortisol production and measuring how much is released. For women taking oestrogen pills (found in birth control and hormone replacement therapy), the test results can be misleading. Oestrogen increases a substance in the blood called cortisol-binding globulin (CBG), which attaches to cortisol and makes some of it inactive. When doctors measure cortisol, they check both active and inactive forms. If CBG is high, the test can falsely suggest cortisol levels are normal, making it harder to tell if the adrenal glands are working correctly. To avoid this problem, women taking oestrogen pills and gels/patches (transdermal) are asked to stop for 6 weeks before the test so that CBG/cortisol levels return to normal. However, this can cause uncomfortable symptoms like hot flushes, mood swings, and headaches. Some women use transdermal oestrogen, which is absorbed through the skin instead. Unlike pills, there is some evidence that transdermal oestrogen doesn't affect CBG levels meaning women using them may not need to stop before an SST. This study will provide more evidence confirming that transdermal oestrogen is safe to continue before testing. We will study three groups: women taking oestrogen pills, women using gel/patches, and women not taking oestrogen. By measuring CBG and cortisol every week, we aim to find out exactly when CBG returns to normal after stopping oestrogen pills. If it happens before 6 weeks, doctors may be able to shorten the break, making testing more manageable and more comfortable. This research could improve testing for women taking oestrogen, potentially allowing those on gel/patches to continue treatment and those on pills to pause for a shorter time before testing.