Cortisol

What is Cortisol?

The body's primary stress hormone, produced by the adrenal glands.

Cortisol regulates metabolism, blood sugar, and blood pressure, and drives the body's stress response. It follows a diurnal rhythm: levels are highest shortly after waking (typically peaking around 6-8am) and decline through the day to their lowest point around midnight.

Tests often checked alongside this

• ACTH — helps identify whether the issue starts in the adrenal glands or the pituitary
• DHEA-S — another adrenal hormone used to assess overall adrenal function
• Free cortisol (saliva or urine) — captures patterns a single blood draw can miss

How this can show up in how you look and feel

• High cortisol can be associated with weight gain around the face or midsection
• Some people notice thinner skin or easier bruising with prolonged elevation
• Poor sleep and mood changes like anxiety can be associated with cortisol imbalance
• Low cortisol is sometimes associated with fatigue and low blood pressure

What can affect this marker

• Time of day it's measured
• Sleep quality and stress levels
• Certain medications, like steroids
• Biotin supplements before testing

What to track over time

• Your rhythm across the day
• Trend across repeat morning tests
• Sleep and stress patterns
• Alongside energy and mood changes

What to ask your doctor

• Was this test timed correctly?
• Should I check my rhythm across the day?
• Could stress be skewing this result?
• Do I need further hormone testing?

This glossary entry is for informational purposes only and is not a substitute for professional medical advice. Read our Terms of Use.