Yes, hypothyroidism can cause elevated cortisol levels. The connection is well established: when thyroid hormone levels drop, your body clears cortisol from your bloodstream more slowly, and your stress-response system becomes more reactive. About 12.5% of hypothyroid patients show cortisol levels above the normal range, but even people with mildly elevated TSH (a marker of underactive thyroid function) tend to have higher cortisol than those with lower TSH values.
Why Low Thyroid Hormones Raise Cortisol
Two overlapping mechanisms drive the connection. The first involves how your liver processes cortisol. Thyroid hormones help regulate the speed at which your body breaks down and eliminates cortisol. When thyroid levels fall, this metabolic clearance rate slows down, meaning cortisol lingers in your blood longer than it should. Even if your adrenal glands are producing a normal amount, the buildup creates higher circulating levels.
The second mechanism involves your brain’s stress-response system, known as the HPA axis. In hypothyroidism, the pituitary gland becomes hypersensitive to the chemical signals that trigger cortisol production. When researchers gave hypothyroid patients a hormone that stimulates the pituitary (called CRH), both ACTH and cortisol responses were significantly greater than in people with normal thyroid function. In other words, the system overreacts to normal stress signals, producing more cortisol than it otherwise would.
Together, these two effects create a double hit: your body makes more cortisol in response to stimulation and clears it more slowly. Research on 24-hour cortisol dynamics in primary hypothyroidism confirms that the elevated levels are “primarily due to decreased metabolic clearance of cortisol and a presumptive decrease in the negative feedback effect of cortisol on the hypothalamo-pituitary axis.” The good news is that these changes are largely reversible with thyroid treatment.
Even Mild Thyroid Changes Affect Cortisol
You don’t need full-blown hypothyroidism for cortisol to creep up. A study of healthy young adults found a significant positive correlation between TSH and cortisol levels, and this relationship held even at TSH levels well below the traditional subclinical hypothyroidism cutoff of 4.5 uIU/L. Specifically, the TSH-cortisol link remained statistically significant down to a TSH of 2.5 uIU/L, only disappearing below 2.0.
This finding is notable because many people with TSH levels between 2.5 and 4.5 are told their thyroid is “normal.” Yet their cortisol levels already trend higher than those of people with lower TSH values. Interestingly, the relationship was tied specifically to TSH rather than to free T3 or T4 levels, suggesting that the pituitary’s stress response may be the more sensitive indicator of early thyroid-cortisol disruption.
Symptoms That Overlap and Confuse
High cortisol and hypothyroidism share a frustrating number of symptoms: weight gain (especially around the midsection), fatigue, brain fog, mood changes, and disrupted sleep. This overlap makes it difficult to tell which condition is driving what. Some people with untreated hypothyroidism develop a physical appearance that looks like Cushing’s syndrome, the condition caused by chronically high cortisol. A round face, central body fat distribution, and fatigue can appear in both.
The features that most reliably point to true Cushing’s syndrome rather than thyroid-related cortisol elevation include easy bruising, facial redness (plethora), significant muscle weakness in the upper legs and arms, and wide reddish-purple stretch marks over 1 cm wide. If you don’t have those specific signs, elevated cortisol in the context of known hypothyroidism is more likely a downstream effect of the thyroid problem itself.
How Treatment Changes the Picture
When hypothyroidism is treated with thyroid hormone replacement, cortisol metabolism speeds back up. Your liver resumes clearing cortisol at a normal rate, and the pituitary’s exaggerated stress response tends to calm down. For most people, this means cortisol levels gradually normalize as thyroid levels stabilize.
There is one important caution. Starting thyroid replacement accelerates cortisol clearance quickly. If someone has an underlying adrenal problem on top of hypothyroidism, this sudden drop in cortisol can be dangerous. This is why clinicians check cortisol levels before initiating thyroid treatment in cases of secondary hypothyroidism (where the pituitary gland itself is the problem). For people with primary hypothyroidism, which accounts for the vast majority of cases, this risk is much lower, but it underscores how tightly linked the two hormone systems are.
What This Means for Cortisol Testing
If you have untreated or undertreated hypothyroidism and your cortisol comes back high, the thyroid problem may be the cause rather than a separate adrenal disorder. Cortisol tests, including 24-hour urine collections and blood draws, can read artificially high when thyroid function is low simply because cortisol isn’t being cleared at its normal rate. This can lead to unnecessary workups for Cushing’s syndrome when the real issue is the thyroid.
The practical takeaway: if your thyroid is not yet well controlled, an elevated cortisol result should be interpreted cautiously. In many cases, optimizing thyroid treatment first and then retesting cortisol gives a much clearer picture of whether the adrenal system is actually overproducing or whether the cortisol elevation was secondary to slow clearance all along.