Does metformin lower or raise cortisol levels?

Metformin Does Not Lower Cortisol—It Actually Increases Cortisol Regeneration

Based on the available evidence, metformin increases cortisol levels by enhancing cortisol regeneration through the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), rather than lowering them. This finding comes from a well-designed randomized controlled trial that directly measured cortisol metabolism using sophisticated deuterated cortisol infusion techniques 1.

The Evidence on Metformin and Cortisol

The most rigorous study examining this relationship was a double-blind, randomized, placebo-controlled crossover trial that measured whole-body cortisol regeneration in obese men with and without type 2 diabetes 1. This study found:

• Metformin increased whole-body cortisol regeneration by 11βHSD1 by approximately 25% compared to both placebo and the sulfonylurea gliclazide
• This effect occurred in both diabetic and non-diabetic obese men
• Hepatic 11βHSD1 activity also tended to increase with metformin treatment
• The mechanism appears to be indirect, as metformin did not increase 11βHSD1 activity when tested directly in hepatocytes or adipocytes in vitro

Additional Supporting Evidence

Other studies provide corroborating information, though with less direct measurement:

• In non-obese women with polycystic ovary syndrome (PCOS), metformin treatment for 6 months did not significantly change basal cortisol levels, but it did modulate cortisol pulsatile release patterns 2
• A study in patients with impaired glucose tolerance found that metformin combined with diet did not alter basal cortisol secretion or the cortisol response to dexamethasone suppression testing 3
• Another study in PCOS patients showed no significant changes in ACTH or cortisol levels after 12 months of metformin treatment 4

Clinical Implications

The increase in cortisol regeneration by metformin may partially offset some of its metabolic benefits, though this does not appear to negate its overall therapeutic value 1. This finding is particularly relevant when considering:

1. Co-prescription with 11βHSD1 inhibitors: The cortisol-increasing effect of metformin may actually enhance the therapeutic target for selective 11βHSD1 inhibitors, potentially improving their efficacy 1

2. Glucocorticoid co-administration: When metformin is used alongside glucocorticoid therapy, it appears to protect against glucocorticoid-induced metabolic toxicity, including insulin resistance, despite the cortisol-regenerating effects 5, 6

3. Overall metabolic profile: The modest increase in cortisol regeneration does not appear to cause clinically significant hypercortisolism or negate metformin's well-established benefits on glucose control, cardiovascular outcomes, and mortality 7, 8

Important Caveats

• The cortisol-increasing effect is modest and indirect, occurring through mechanisms that remain incompletely understood
• This effect does not translate to clinically apparent Cushing's syndrome or significant adverse outcomes in routine clinical use
• The metabolic benefits of metformin (improved insulin sensitivity, weight neutrality, cardiovascular protection) remain robust and well-documented across multiple guidelines 9, 7, 8
• Metformin remains the preferred first-line pharmacologic agent for type 2 diabetes unless contraindicated 7

In summary, metformin raises rather than lowers cortisol through increased regeneration by 11βHSD1, but this effect is modest and does not diminish its role as a foundational therapy for type 2 diabetes.