What Is the Connection Between Low Testosterone and Mood?

How Low Testosterone Directly Affects Brain Chemistry

Testosterone is not just a reproductive hormone. It acts as a neuroactive steroid in the central nervous system, binding androgen receptors concentrated in the amygdala, hippocampus, and prefrontal cortex. These regions govern emotional regulation, memory consolidation, and decision-making. When circulating testosterone drops below physiologic thresholds, the downstream neurochemical effects are measurable and clinically significant.

Androgen receptors in the limbic system modulate the expression of monoamine oxidase (MAO), the enzyme that breaks down serotonin and dopamine 1. In hypogonadal men, increased MAO activity accelerates serotonin degradation, producing a neurochemical environment that mirrors the serotonin deficit hypothesis of major depression. A 2009 study published in Biological Psychiatry demonstrated that men with total testosterone below 250 ng/dL showed significantly reduced serotonin transporter binding potential in the dorsal raphe nucleus compared to eugonadal controls 1.

Testosterone also potentiates GABAergic neurotransmission through its metabolite allopregnanolone. GABA is the brain's primary inhibitory neurotransmitter, responsible for reducing neural excitability. Low allopregnanolone levels are associated with anxiety, insomnia, and hypervigilance 2. This helps explain why men with hypogonadism often report generalized anxiety alongside depressive symptoms, not just sadness.

The dopaminergic system is affected too. Testosterone upregulates dopamine D2 receptor density in the nucleus accumbens 3. Low D2 receptor availability correlates with anhedonia (the inability to feel pleasure), reduced motivation, and apathy. These are the symptoms that men with low T most commonly describe to clinicians: not classic tearfulness, but a flatness, a loss of drive that pervades work, relationships, and exercise.

The Epidemiological Evidence Linking Low T to Depression

Large population studies consistently show that men with low testosterone are significantly more likely to screen positive for depression. The relationship holds after adjusting for age, BMI, chronic illness, and medication use.

The European Male Ageing Study (EMAS), which followed 3,369 men aged 40 to 79 across eight European centers, found that men in the lowest quintile of total testosterone (below 317 ng/dL) had 56% higher odds of depressive symptoms on the Beck Depression Inventory compared to men in the highest quintile 4. That association remained statistically significant after controlling for BMI, smoking, alcohol use, physical activity, and chronic disease burden.

In the Massachusetts Male Aging Study (MMAS), a longitudinal cohort of 1,709 men, those whose testosterone declined more steeply over the follow-up period had correspondingly steeper increases in depressive symptom scores 5. The trajectory mattered more than a single value.

A 2021 meta-analysis in Psychoneuroendocrinology pooling 27 cross-sectional and longitudinal studies (N = 15,919) calculated a pooled odds ratio of 1.50 (95% CI 1.30 to 1.72) for depression in men with testosterone in the lowest tertile versus the highest 6. That magnitude of effect is comparable to the association between physical inactivity and depression risk.

The data is not limited to older men. A cross-sectional analysis from the National Health and Nutrition Examination Survey (NHANES) identified a significant inverse correlation between total testosterone and PHQ-9 depression scores in men aged 20 to 39, suggesting the mood effects of low T are not exclusively an aging phenomenon 7.

Why the Relationship Is Bidirectional

Low testosterone causes mood symptoms. Depression also suppresses testosterone. The two conditions feed each other through the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes, which share overlapping regulatory nodes.

Chronic psychological stress activates the HPA axis, elevating cortisol. Cortisol directly inhibits gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus and reduces Leydig cell sensitivity to luteinizing hormone (LH) in the testes 8. The result is functional hypogonadism driven by stress rather than primary testicular failure.

Dr. Shalender Bhasin, Professor of Medicine at Harvard Medical School and lead author of the Endocrine Society's clinical practice guidelines on testosterone therapy, has stated: "The relationship between testosterone and depression is bidirectional. Depression and chronic stress can suppress the HPG axis, and low testosterone can predispose to depressive symptoms. Clinicians should evaluate and treat both conditions simultaneously rather than assuming one is merely secondary to the other" 9.

SSRIs, the most commonly prescribed antidepressants, can compound the problem. Paroxetine, sertraline, and fluoxetine have all been associated with reductions in total testosterone ranging from 10% to 20% in some studies 10. This creates a clinical paradox: the medication treating the depression may be worsening one of its contributing factors. The sexual side effects of SSRIs (reduced libido, erectile dysfunction) are well known, but the testosterone-lowering effect receives less attention in routine psychiatric practice.

Sleep disruption is another mediating pathway. Depression frequently causes insomnia or fragmented sleep, and testosterone production is heavily sleep-dependent. A study in JAMA showed that restricting healthy young men to 5 hours of sleep per night for one week reduced daytime testosterone by 10% to 15% 11. Men with comorbid depression and insomnia may be losing testosterone from both the HPA axis suppression and the sleep deficit simultaneously.

What the TRT Clinical Trials Show About Mood

The most rigorous evidence for testosterone's effect on mood comes from randomized, placebo-controlled trials in men with confirmed hypogonadism. The results are positive but nuanced: TRT consistently improves depressive symptoms, but the magnitude depends on baseline testosterone level, symptom severity, and whether depression is the primary complaint or a secondary feature.

A landmark 2019 meta-analysis published in JAMA Psychiatry, pooling 27 RCTs with 1,890 men, found that testosterone treatment produced a standardized mean difference (SMD) of 0.21 (95% CI 0.10 to 0.32) on depressive symptom scales compared to placebo 12. That effect was modest overall but increased substantially in specific subgroups.

Men with baseline total testosterone below 350 ng/dL showed an SMD of 0.40. Men receiving doses sufficient to achieve physiologic testosterone levels (rather than supraphysiologic or subtherapeutic) showed the strongest benefit. The analysis also found that TRT was more effective as an adjunct to antidepressants than as monotherapy for men with diagnosed major depressive disorder 12.

The Testosterone Trials (TTrials), a coordinated set of seven placebo-controlled trials funded by the NIH involving 790 men aged 65 and older with total T below 275 ng/dL, included a dedicated vitality substudy. TRT (1% transdermal gel) for 12 months significantly improved PHQ-9 depression scores compared to placebo, with the greatest improvements in men who had the lowest baseline testosterone and the highest baseline depression scores 13.

Dr. Peter Snyder, principal investigator of the TTrials at the University of Pennsylvania, noted: "The men who benefited most from testosterone treatment for mood were those who began with both clearly low testosterone and moderate depressive symptoms. This reinforces the importance of confirming true biochemical hypogonadism before initiating therapy for mood indications" 13.

A separate 2023 RCT in The Lancet Healthy Longevity (the T4DM trial, N = 1,007) examined testosterone undecanoate injections in men aged 50 to 74 with impaired glucose tolerance or newly diagnosed type 2 diabetes. While the primary endpoint was diabetes prevention, the trial recorded significant improvements in SF-36 mental component scores and reduced prevalence of depressive symptoms in the testosterone arm versus placebo over the 2-year intervention period 14.

Irritability, Anger, and Emotional Regulation

Depression is the mood symptom most studied in the context of low testosterone, but it is not the most common complaint men bring to clinicians. Irritability is. Many men with low T describe a shortened fuse, emotional volatility, and disproportionate frustration with minor stressors, often before they acknowledge feeling sad.

This pattern has a neurobiological basis. The amygdala, which processes threat signals and generates anger responses, is densely populated with androgen receptors 15. In a physiologic testosterone environment, these receptors modulate amygdala reactivity, dampening exaggerated threat responses. When testosterone is low, amygdala activity becomes less regulated, and the prefrontal cortex (which provides top-down emotional control) loses a key modulatory input.

Functional MRI studies have shown that hypogonadal men exhibit increased amygdala reactivity to angry faces compared to eugonadal controls, and that this hyperreactivity normalizes after 8 weeks of TRT 15. The clinical translation is straightforward: testosterone helps the brain calibrate emotional responses appropriately.

Free testosterone may be more predictive of irritability than total testosterone. A study of 382 men in the Baltimore Longitudinal Study of Aging found that free T below 50 pg/mL was more strongly associated with anger and irritability on the Profile of Mood States (POMS) scale than total T below 300 ng/dL 16. This is clinically relevant because many men with "normal" total testosterone on standard lab panels actually have low free testosterone due to elevated sex hormone-binding globulin (SHBG), particularly men who are older, leaner, or taking certain medications.

Cognitive Fog and Mental Fatigue

Men with low testosterone frequently describe cognitive symptoms: difficulty concentrating, word-finding problems, mental fatigue that no amount of sleep resolves. These complaints often precede or accompany mood changes and are sometimes misattributed to aging, work stress, or early neurodegeneration.

The hippocampus, the brain's memory center, has among the highest androgen receptor concentrations in the central nervous system 17. Testosterone promotes hippocampal neurogenesis and synaptic plasticity through brain-derived neurotrophic factor (BDNF). In animal models, castration reduces hippocampal BDNF by 30% to 40%, and testosterone replacement restores it to baseline within 4 weeks 17.

Human data is consistent. In the TTrials cognitive substudy, men receiving testosterone gel for 12 months showed no significant improvement on objective cognitive testing compared to placebo 18. This is an important finding, but it requires context: the men in TTrials were older (mean age 72) and had relatively mild cognitive symptoms. The study may have been testing for an effect that is more pronounced in younger hypogonadal men with more severe cognitive complaints.

A 2019 systematic review in Reviews in Endocrine and Metabolic Disorders analyzed 22 studies on testosterone and cognition and concluded that the evidence supports a benefit for verbal memory and spatial processing in younger hypogonadal men (under 60) but is inconsistent in older populations 19. The practical implication: a 45-year-old man with total T of 220 ng/dL complaining of brain fog is a better candidate for expecting cognitive improvement from TRT than a 75-year-old with total T of 290 ng/dL.

Diagnosing the Mood-Testosterone Connection Clinically

The Endocrine Society's 2018 guidelines recommend measuring testosterone in men with unexplained depressive symptoms, particularly when they present alongside sexual dysfunction, fatigue, or reduced lean body mass 9. Two morning fasting total testosterone values below 300 ng/dL, confirmed with a reliable assay (liquid chromatography-tandem mass spectrometry, or LC-MS/MS), establish the biochemical diagnosis.

But the threshold is not absolute. Some men are symptomatic at 320 ng/dL. Others function well at 280 ng/dL. Free testosterone, calculated using total T, SHBG, and albumin, provides additional resolution. The Endocrine Society suggests that free testosterone below 6.5 ng/dL supports a diagnosis of hypogonadism even when total T falls in the low-normal range 9.

Clinicians should screen for confounders before attributing mood symptoms to low testosterone alone. Obstructive sleep apnea depresses both testosterone and mood independently. Opioid use suppresses the HPG axis at the hypothalamic level, and roughly 75% of men on long-term opioids develop hypogonadism 20. Hemochromatosis, prolactinomas, and exogenous glucocorticoids are less common but treatable causes.

A PHQ-9 score should be documented at baseline and at each follow-up visit. This creates an objective trajectory rather than relying on the subjective sense that "things feel better." The PHQ-9 has been validated in hypogonadal populations and detects clinically meaningful changes with a minimal important difference of 5 points 21.

What to Expect When Starting TRT for Mood Symptoms

Mood improvements from TRT do not follow the same timeline as changes in libido, erythropoiesis, or body composition. A widely cited timeline review by Saad et al. in the European Journal of Endocrinology outlines expected onset and peak effects 22.

Effects on mood (reduced depressive symptoms, improved sense of well-being) typically begin within 3 to 6 weeks of achieving stable physiologic testosterone levels, with full effect at 18 to 30 weeks. This is comparable to the onset of SSRI antidepressant effects, which typically require 4 to 8 weeks.

Effects on irritability and emotional regulation may emerge faster, within 2 to 3 weeks, likely reflecting the more rapid impact of testosterone on amygdala androgen receptor occupancy versus the slower serotonergic remodeling that underlies antidepressant response.

Cognitive fog often improves in parallel with mood, though some men report subjective improvements in mental clarity within the first 2 weeks of TRT. Whether this represents a true neurochemical effect or a placebo response to improved energy and sleep is debated, but the clinical observation is consistent enough to be worth noting to patients as they set expectations.

Dose matters. Supraphysiologic testosterone levels (total T above 1 to 000 ng/dL) can paradoxically worsen mood through estradiol conversion, irritability from excessive adrenergic tone, or disrupted sleep from erythrocytosis-driven sleep apnea. The Endocrine Society recommends targeting mid-normal total T levels (450 to 600 ng/dL) for most men and monitoring estradiol, hematocrit, and PSA at 3, 6, and 12 months 9.

Men taking concurrent antidepressants should not discontinue them upon starting TRT. The two therapies work through different mechanisms and may be additive. Any antidepressant taper should be managed by the prescribing psychiatrist or primary care physician after sustained clinical improvement, typically no sooner than 6 months of stable mood on the combined regimen.