Can low Thyroid-Stimulating Hormone (TSH) levels increase testosterone levels in patients with hyperthyroidism?

Low TSH Does Not Increase Testosterone—It Actually Decreases It

In hyperthyroidism (low TSH), testosterone levels paradoxically increase due to elevated SHBG binding more testosterone, but free (bioavailable) testosterone actually decreases, leading to functional hypogonadism despite higher total testosterone measurements. 1

The Biochemical Mechanism

What Happens to Testosterone in Hyperthyroidism

• Total testosterone rises because thyroid hormone excess stimulates hepatic production of sex hormone-binding globulin (SHBG), which binds testosterone tightly 2, 1
• Free testosterone concentration remains unchanged or decreases in men with hyperthyroidism, despite the elevated total testosterone 1
• Non-SHBG-bound testosterone (the bioavailable fraction) significantly decreases during thyrotoxicosis 1
• The percentage of free testosterone drops significantly when TSH is suppressed 1

The SHBG Connection

• SHBG concentration correlates directly with the severity of thyrotoxicosis—the lower the TSH and higher the thyroid hormones, the more SHBG increases 1
• This SHBG elevation traps testosterone in an inactive, bound form that cannot enter cells or exert androgenic effects 1
• When hyperthyroidism is treated and TSH normalizes, SHBG gradually decreases over months, but recovery lags behind normalization of thyroid function 2

Clinical Manifestations in Men

Reproductive Dysfunction

• Men with hyperthyroidism demonstrate higher rates of asthenozoospermia (poor sperm motility), oligozoospermia (low sperm count), and teratozoospermia (abnormal sperm morphology) 3
• Sexual dysfunction, particularly premature ejaculation, occurs more frequently in hyperthyroid men 3
• LH response to GnRH is hyperresponsive in hyperthyroidism, but response to hCG is subnormal, indicating both central and testicular dysfunction 4

Hormonal Changes

• Estradiol levels rise in hyperthyroid men due to increased aromatization of testosterone to estrogen 4
• Gynecomastia is common in men with thyrotoxicosis, resulting from the elevated estradiol-to-testosterone ratio 4
• DHT (dihydrotestosterone) and its metabolites are elevated in hyperthyroid women, indicating increased 5α-reductase activity 2

The Opposite Effect: Hypothyroidism and Testosterone

Primary Hypothyroidism (High TSH)

• Free testosterone concentrations are reduced in men with primary hypothyroidism 4
• This occurs through hypogonadotropic hypogonadism—the hypothalamus/pituitary fails to adequately stimulate the testes 4
• LH response to GnRH is subnormal in hypothyroid men 4
• Thyroid hormone replacement normalizes free testosterone concentrations 4

Subclinical Hypothyroidism

• Even subclinical hypothyroidism (TSH <10 mIU/L with normal free T4) is associated with decreased serum testosterone 5
• Progesterone (testosterone's precursor) also decreases, suggesting impaired steroidogenesis 5
• The testosterone-to-estradiol conversion rate increases to maintain estradiol levels, further depleting testosterone 5
• Prolactin levels are slightly but significantly elevated in subclinical hypothyroidism, which may contribute to hypogonadism 5

Critical Clinical Pitfalls

Don't Be Fooled by Total Testosterone

• Measuring only total testosterone in hyperthyroid patients will show falsely elevated levels that do not reflect the true androgenic status 1
• Always measure free testosterone or calculate the free androgen index (total testosterone/SHBG × 100) to assess true bioavailable hormone 1
• The discrepancy between total and free testosterone is greatest when thyrotoxicosis is most severe 1

Immune Checkpoint Inhibitor Considerations

• Patients on immunotherapy can develop hypophysitis with simultaneous low TSH and low testosterone due to pituitary destruction 6
• This represents central hypogonadism plus central hypothyroidism, not the peripheral effects described above 6
• Always check 9 AM cortisol when TSH is abnormal in immunotherapy patients, as adrenal insufficiency commonly coexists 6
• If hypophysitis is suspected, start corticosteroids before thyroid hormone replacement to prevent adrenal crisis 6, 7

Recovery Timeline

• When hyperthyroidism is treated, androgen levels normalize within 3 months, but SHBG remains elevated for at least 6 months 2
• This time lag means that free testosterone may remain suppressed even after thyroid function normalizes 2
• Patients may continue experiencing hypogonadal symptoms during this recovery period despite euthyroidism 2

Diagnostic Approach When Both Are Abnormal

If TSH is Low and Testosterone is Low

• Measure free T4 and free T3 to confirm hyperthyroidism versus central hypothyroidism 8
• Check FSH and LH to distinguish primary testicular failure from central hypogonadism 8
• If FSH is elevated with low testosterone, consider pituitary MRI to exclude adenoma or hypophysitis 8
• Comprehensive hormonal testing including ACTH and cortisol is essential when evaluating suspected hypophysitis 8

If TSH is High and Testosterone is Low

• This represents primary hypothyroidism causing secondary hypogonadism 4, 5
• Thyroid hormone replacement will normalize testosterone without need for testosterone therapy 4
• Recheck testosterone 3-6 months after achieving euthyroidism before considering testosterone replacement 4

The Bottom Line

Low TSH from hyperthyroidism does not increase functional testosterone—it creates a state of biochemical hypogonadism masked by elevated total testosterone. The key is understanding that SHBG elevation renders most of the testosterone biologically inactive. In contrast, high TSH from hypothyroidism directly suppresses testosterone production through central mechanisms. Both thyroid disorders impair male reproductive function, but through opposite mechanisms that require different management approaches.