Testosterone has a clearer effect on sexual function than on motivation. It can look like the biological basis of such drive—or the lack thereof. Yet the Endocrine Society's 2018 guideline identifies low energy and motivation as nonspecific symptoms with many possible causes.
How Testosterone Affects Drive, Energy and Mood
Testosterone treatment improves sexual function more clearly than energy or mood. Snyder and colleagues' 2016 Testosterone Trials were seven coordinated placebo-controlled trials in 790 men aged 65 or older.
All had testosterone below 275 ng/dL with symptoms and used testosterone or placebo gel for one year. Sexual activity, desire, and erectile function improved. Vitality, measured on a fatigue scale, showed no significant benefit, and mood improved slightly. The trials therefore found testosterone's clearest effects in sexual function, not energy.
Signs of Low Testosterone
The Endocrine Society's guideline reserves a diagnosis of hypogonadism, or clinically low testosterone, for men with symptoms and repeatedly low fasting morning total testosterone. Its symptom table lists loss of body hair and very small testes as specific signs.
Reduced sexual desire and fewer spontaneous erections are suggestive. Low energy and motivation, poor concentration and sleep disturbance are nonspecific.
The guideline's lower limit of normal is 264 ng/dL in healthy nonobese young men. The American Urological Association (AUA) guideline uses a cutoff below 300 ng/dL, found on at least two tests. Obesity lowers sex hormone-binding globulin (SHBG), the protein that carries testosterone in blood, so free testosterone, the unbound portion, may need measuring. Symptoms alone therefore cannot identify low testosterone.
Testosterone and Mood
The evidence that giving testosterone causes aggression is weak. In Geniole and colleagues' 2020 meta-analysis, giving testosterone had a weak and statistically nonsignificant effect on aggression.
A separate article examines whether testosterone makes men angry. Neither these data nor the slight mood gain in the Testosterone Trials shows that testosterone controls a man's drive.
Sleep and Testosterone
Short sleep lowers testosterone, and severe sleep apnea is associated with lower levels. In a 2011 laboratory study in JAMA, Leproult and Van Cauter limited 10 healthy young men to five hours in bed for eight nights. Daytime testosterone fell by 10% to 15%. Vigor also fell, a change the study cannot attribute to testosterone.
Su and colleagues' 2022 meta-analysis found lower testosterone in men with obstructive sleep apnea (OSA), in which breathing repeatedly stops during sleep. The difference was significant only when the apnea was severe.
In December 2024, the Food and Drug Administration (FDA) approved Zepbound, a weight-loss drug, for moderate-to-severe OSA in adults with obesity. The relationship between sleep and body weight has its own article. Poor sleep lowers testosterone and can also explain tiredness on its own.
Obesity and Low Testosterone
Obesity is probably the condition most often found with low testosterone in men, according to Dhindsa and colleagues. Their 2010 Diabetes Care study measured free testosterone in 1,849 American men aged 45 or older. Among men without diabetes, subnormal levels occurred in 26% of lean, 29% of overweight and 40% of obese men.
In Fui and colleagues' 2014 review, moderate obesity lowers SHBG through insulin resistance and so reduces total testosterone. Severe obesity also suppresses the brain hormones that stimulate the testes.
Corona and colleagues' 2013 meta-analysis pooled 24 studies. Total testosterone rose about 83 ng/dL after low-calorie diets and 252 ng/dL after bariatric surgery. The amount of weight lost best predicted the rise. Obesity-related low testosterone is thus functional hypogonadism, caused by another condition and potentially reversible with substantial weight loss.
Does Weight Loss on Tirzepatide Raise Testosterone?
Weight loss on tirzepatide probably does raise testosterone in men with obesity, but no randomized trial has tested this. Tirzepatide is a once-weekly injection that stimulates receptors for two gut hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1).
La Vignera and colleagues' 2025 Italian study of men with obesity and low testosterone was small, two months long and not randomized. Allocation depended partly on preference and ability to pay.
With diet and walking, median total testosterone rose from 186.5 to 424 ng/dL in 28 men who added low-dose tirzepatide. On diet and walking alone, it rose from 192 to 266 ng/dL in 30 men. Salvio and colleagues' 2025 meta-analysis of GLP-1 drugs found testosterone rose with weight loss but could not show a direct effect on the testes.
Neither of Eli Lilly's tirzepatide labels lists low testosterone as an approved use. Zepbound is labeled for chronic weight management and OSA, and Mounjaro for patients with type 2 diabetes.
Compounded tirzepatide, mixed by pharmacies without FDA approval or review, has no testosterone data, and trial results do not apply to it. Pharmacy copies are now restricted because FDA declared the tirzepatide shortage over on December 19, 2024. In tirzepatide treatment , a testosterone rise is a likely by-product of weight loss, not a reason to choose the drug.
When TRT Is an Option
Testosterone replacement therapy (TRT) is for men with symptoms and consistently low levels. In obesity-related deficiency, Grossmann and Matsumoto's 2017 review advises starting it alongside or after weight-loss efforts. The Endocrine Society advises against it in untreated severe sleep apnea and for men planning children soon, as it reduces sperm production.
Lincoff and colleagues' 2023 TRAVERSE trial randomized 5,246 men aged 45 to 80 with low testosterone and existing heart disease or high heart risk. It tested noninferiority, meaning testosterone had only to prove no worse than placebo. Over a mean 33 months, major heart events occurred in 7.0% on testosterone and 7.3% on placebo.
That result showed noninferiority, not benefit. Atrial fibrillation, acute kidney injury, and pulmonary embolism were more common with testosterone. FDA added a class-wide blood pressure warning in 2025. In June 2026, it asked manufacturers to remove label wording saying TRT's safety and benefit in age-related low testosterone had not been established.
When drive is low, obesity and poor sleep are the causes to check first, and testosterone treatment is for confirmed deficiency.
Sources
- Testosterone, energy and mood: Snyder et al., N Engl J Med (Testosterone Trials), 2016
- Diagnosis: Endocrine Society Testosterone Therapy Guideline, 2018; AUA Testosterone Deficiency Guideline, 2018
- Aggression: Geniole et al., Horm Behav, 2020
- Sleep: Leproult and Van Cauter, JAMA, 2011; Su et al., Andrology, 2022; FDA Zepbound Sleep Apnea Approval, 2024
- Obesity: Dhindsa et al., Diabetes Care, 2010; Fui et al., Asian J Androl, 2014; Corona et al., Eur J Endocrinol, 2013
- Tirzepatide: La Vignera et al., Reprod Biol Endocrinol, 2025; Salvio et al., Andrology, 2025; Zepbound label, 2026; Mounjaro label, 2026; FDA Concerns with Unapproved GLP-1 Drugs, 2026; FDA Clarifies Policies for Compounders, 2026
- Testosterone therapy: Grossmann and Matsumoto, J Clin Endocrinol Metab, 2017; Lincoff et al., N Engl J Med (TRAVERSE), 2023; FDA Class-Wide Labeling Changes for Testosterone Products, 2025; FDA Testosterone Information, 2026