Does Testosterone Improve Memory? What the Randomized Trials Show About Brain Fog, Cognition and TRT in Men Over 40
Men with low testosterone develop dementia more often. Yet when researchers gave older men testosterone for one to three years, their memory scores moved exactly as much as the placebo group's did.
Testosterone therapy has not improved memory in the largest placebo-controlled trials of older men with low testosterone. Observational data still link low testosterone to more dementia, which is why researchers now treat a low level as a warning sign rather than a proven memory fix.
Does testosterone improve memory? In the two largest placebo-controlled trials of older men with low testosterone, it did not. The Testosterone Trials Cognitive Function Trial, published by Susan Resnick and colleagues in JAMA in 2017, gave testosterone gel or placebo gel to 788 men aged 65 or older for one year, and delayed paragraph recall improved by the same amount in both groups. The TEAAM trial, published by Grace Huang and colleagues in Lancet Diabetes and Endocrinology in 2016, ran for 3 years and also found no cognitive benefit.
The question keeps coming up because low testosterone and poor memory travel together. In the UK Biobank, men in the lowest fifth of total testosterone had a 43% higher rate of dementia than men in the highest fifth. Brain fog is also one of the most common complaints that sends men to get their testosterone checked. The trial data and the observational data point in different directions, and the gap between them is what this article explains.
-0.07
TTrials Difference In Delayed Recall, Testosterone vs Placebo
493 men with age-associated memory impairment, P = .88, Resnick 2017, JAMA
36 months
TEAAM Testosterone Gel Treatment, No Cognitive Benefit
308 men aged 60 and older, Huang 2016, Lancet Diabetes and Endocrinology
1.43
Dementia Hazard Ratio, Lowest vs Highest Testosterone Fifth
159,411 men in UK Biobank, Marriott 2022, Alzheimer's and Dementia
0.14
Executive Function Effect Size Across 14 Trials
Small effect in cognitively healthy older men, Tan 2019 meta-analysis
-0.67
Visuomotor Effect Size In Men On Androgen Deprivation
No significant effect in the other six domains, McGinty 2014 meta-analysis
Does Testosterone Improve Memory in Older Men With Low Testosterone?
Testosterone did not improve memory in the Testosterone Trials, the largest test of the question so far. The Testosterone Trials (TTrials) were 7 coordinated trials run at 12 US academic medical centers. All 788 men were 65 or older, had a serum testosterone below 275 ng/dL, and had problems with sexual function, physical function or vitality. Half (394) used testosterone gel adjusted to keep their level in the normal range for young men, and half (394) used placebo gel, for one year.
The TTrials memory analysis focused on the 493 men who met criteria for age-associated memory impairment, meaning they both complained about their memory and scored below normal on objective tests. Their mean age was 72.3 and their mean baseline testosterone was 234 ng/dL. Of these men, 247 received testosterone and 246 received placebo. The main outcome was delayed paragraph recall, a test in which a man hears a short story and retells it later, scored from 0 to 50.
TTrials: Delayed Paragraph Recall Scores Over 12 Months (Score Range 0 to 50)
- Testosterone gel
- Placebo gel
The chart above plots the mean scores reported in the Resnick 2017 JAMA abstract. Both groups improved by about two points, most likely because men get better at a test the second and third time they take it. The adjusted difference between testosterone and placebo was -0.07 points (P = .88), which is effectively zero. Testosterone also showed no significant effect on visual memory, executive function or spatial ability. The authors concluded that one year of testosterone was not associated with improved memory or other cognitive functions in these men.
Does Longer Testosterone Treatment Help Cognition?
A longer course of testosterone did not help either. The TEAAM trial (Testosterone Effects on Atherosclerosis Progression in Aging Men) enrolled 308 men aged 60 and older at 3 medical centres in Boston, Phoenix and Los Angeles. The men had low or low-to-normal testosterone and were randomly assigned to 7.5 g of 1% testosterone gel daily (156 men) or placebo gel (152 men) for 3 years, with the dose adjusted to push testosterone into the mid-normal range.
TEAAM clearly raised hormone levels. Mean total testosterone in the treated group went from 10.6 nmol/L to 19.7 nmol/L, while the placebo group stayed flat at 10.7 and 11.1 nmol/L. Across 280 men with baseline cognitive testing, there were no between-group differences in visuospatial ability, verbal fluency, verbal memory, manual dexterity, or attention and executive function. Changes in cognitive scores were not related to changes in total testosterone, free testosterone or estradiol.
The Two Largest Testosterone Cognition Trials Compared
| Feature | TTrials Cognitive Function Trial | TEAAM |
|---|---|---|
| Publication | Resnick 2017, JAMA | Huang 2016, Lancet Diabetes and Endocrinology |
| Men enrolled | 788 men aged 65 or older | 308 men aged 60 or older |
| Testosterone at entry | Below 275 ng/dL plus symptoms | Low or low-to-normal |
| Treatment | Testosterone gel vs placebo gel | 7.5 g of 1% testosterone gel vs placebo gel |
| Duration | 1 year | 3 years |
| Memory result | No difference in delayed paragraph recall (P = .88) | No difference in verbal memory |
| Other domains | No difference in visual memory, executive function, spatial ability | No difference in visuospatial ability, fluency, dexterity, attention |
Why Is Low Testosterone Linked to Dementia If Treatment Does Not Help?
Low testosterone is consistently associated with dementia in large observational studies. The UK Biobank analysis, published by Ross Marriott, Bu Yeap and colleagues in Alzheimer's and Dementia in 2022, followed 159,411 community-dwelling men with a median age of 61 for 7 years. During that time 826 men developed dementia, including 288 with Alzheimer's disease.
UK Biobank: Hazard Ratios in Men With the Lowest vs Highest Total Testosterone
The UK Biobank numbers translate to about a 43% higher dementia rate and an 80% higher Alzheimer's rate in the lowest testosterone group. The same study found that lower sex hormone-binding globulin (SHBG) was linked to less dementia, with a hazard ratio of 0.66. The authors wrote that additional research is needed to determine causality, because an association in a cohort cannot show that the hormone itself protects the brain.
Several explanations fit both sets of findings. Obesity, diabetes, poor sleep and chronic illness all lower testosterone and also raise dementia risk, so low testosterone may be a marker of a less healthy body rather than a cause of brain ageing. Bu Yeap and Leon Flicker reached this conclusion in a 2022 review in Reviews in Endocrine and Metabolic Disorders, writing that lower testosterone in ageing men should be regarded as a biomarker rather than a proven therapeutic target for reducing cognitive decline and dementia.
A Marker, Not a Proven Lever
Low testosterone in an older man is worth taking seriously, because in the UK Biobank it came with a higher dementia rate. But the trials that raised testosterone for one to three years did not move memory scores. The practical reading is that a low result should prompt a look at the conditions that often sit behind it, such as weight, blood sugar and sleep, rather than a prescription aimed at memory. Any decision about testosterone therapy belongs with a clinician who knows the full picture.
What Do Meta-Analyses of Testosterone and Cognition Show?
Meta-analyses find small effects at best, concentrated in executive function rather than memory. A 2019 meta-analysis in the American Journal of Geriatric Psychiatry by Tan and colleagues pooled 14 randomized trials in cognitively healthy older men. Testosterone produced a small improvement in executive function, with an effect size (Hedges' g) of 0.14. After removing two studies where testosterone levels did not rise, small effects also appeared for the overall cognitive composite (0.18) and psychomotor speed (0.22). There were no significant differences for global cognition, attention, verbal memory, visuospatial ability or visuospatial memory.
A 2025 meta-analysis by Wang and colleagues in Biomedical Reports reached a more positive headline. It pooled 14 studies of androgen replacement in men with hypogonadism and reported a standardized mean difference of 0.454 for overall cognition, with larger effects for executive function and memory than for attention and visuospatial ability. The same paper detected publication bias, meaning small positive studies are more likely to be published than small negative ones, and the authors called for further research with standardized cognitive tests.
Wang 2025 Meta-Analysis: Pooled Effect Sizes by Cognitive Domain (Hypogonadal Men)
The two meta-analyses disagree mostly because they pooled different studies and different men. The Wang analysis looked at men with diagnosed hypogonadism and mixed many smaller studies, while the TTrials and TEAAM trials were large, double-blind and placebo-controlled. When a large well-run trial and a pooled set of smaller studies disagree, the large trial is usually the better guide for what a typical older man can expect.
What Happens to Cognition When Testosterone Is Shut Off?
Shutting testosterone off almost completely affects some thinking skills, but not memory. Men with prostate cancer often receive androgen deprivation therapy (ADT), which drives testosterone to very low levels. A 2014 meta-analysis by McGinty and colleagues in Supportive Care in Cancer pooled 14 studies with 417 men on ADT. Men on ADT performed worse on visuomotor tasks, with an effect size of -0.67 in 193 men, and showed no significant effect in the other six domains, which included verbal memory and visual memory.
The ADT data suggest testosterone plays some role in brain function, but the effect seen in near-total deprivation is narrow. That makes it less surprising that nudging a modestly low level up to the normal range did not change memory in the TTrials or TEAAM.
How the Evidence Stacks Up
Observation
Low T linked to dementia
UK Biobank: higher dementia and Alzheimer's rates in the lowest testosterone fifth
Deprivation
ADT narrows one skill
Visuomotor performance falls; memory domains not significantly affected
Treatment trials
Raising T does not help memory
TTrials (1 year) and TEAAM (3 years) found no cognitive benefit
Current view
Biomarker, not target
Yeap and Flicker 2022: low testosterone signals risk but is not a proven treatment target
Can TRT Help Brain Fog?
Brain fog has not been tested directly as an outcome in the major testosterone trials, so the evidence is limited. Brain fog is a loose description that can include poor focus, low energy, low mood and slow thinking. The TTrials found no improvement in objective memory, executive function or spatial ability, which covers much of what men mean by the term. Men who feel sharper on testosterone may be noticing changes in energy, mood or sleep rather than in measured cognition, and that has not been established in trials.
Fogginess in a man over 40 has many common causes that overlap with low testosterone, including sleep apnea, depression, poorly controlled blood sugar, thyroid problems, heavy drinking and certain medications. Each of these can lower a testosterone reading and slow thinking at the same time. Testosterone24 covers several of them in detail, including the links between low testosterone and depression and between sleep apnea and testosterone.
Questions to Work Through With a Clinician About Memory and Testosterone
First
- ✓Note whether the issue is forgetting, slow thinking, poor focus or low energy
- ✓Ask whether a formal memory screen is worthwhile
- ✓List every medication and supplement, including sleep aids and pain relievers
Next
- ✓Ask about screening for sleep apnea, depression, thyroid problems and blood sugar
- ✓Repeat a low testosterone result with a fasting morning test before acting on it
- ✓Review alcohol intake and sleep length honestly
If testosterone is discussed
- ✓Recognise that the large trials did not find a memory benefit
- ✓Agree on the specific symptoms testosterone therapy is meant to address
- ✓Plan how blood counts and other safety markers will be monitored
Ongoing
- ✓Keep blood pressure, blood sugar and weight in a healthy range
- ✓Stay physically active and socially engaged
- ✓Report any worsening memory promptly rather than waiting
This article is for educational purposes only and is not medical advice. Nothing here diagnoses, treats, cures or prevents any disease, including dementia, Alzheimer's disease or hypogonadism. Testosterone therapy is a prescription treatment discussed only in terms of what published research reported. Speak with a licensed physician before starting, stopping or changing any medication.
Sources
- Resnick SM et al. Testosterone Treatment and Cognitive Function in Older Men With Low Testosterone and Age-Associated Memory Impairment. JAMA, 2017. https://doi.org/10.1001/jama.2016.21044
- Huang G et al. Effects of long-term testosterone administration on cognition in older men with low or low-to-normal testosterone concentrations (TEAAM). Lancet Diabetes and Endocrinology, 2016. https://doi.org/10.1016/S2213-8587(16)30102-4
- Marriott RJ et al. Lower serum testosterone concentrations are associated with a higher incidence of dementia in men: The UK Biobank prospective cohort study. Alzheimer's and Dementia, 2022. https://doi.org/10.1002/alz.12529
- Tan S et al. Effects of Testosterone Supplementation on Separate Cognitive Domains in Cognitively Healthy Older Men: A Meta-analysis. American Journal of Geriatric Psychiatry, 2019. https://doi.org/10.1016/j.jagp.2019.05.008
- Wang B et al. Effects of androgen replacement therapy on cognitive function in patients with hypogonadism: A systematic review and meta-analysis. Biomedical Reports, 2025. https://doi.org/10.3892/br.2025.1983
- Yeap BB, Flicker L. Testosterone, cognitive decline and dementia in ageing men. Reviews in Endocrine and Metabolic Disorders, 2022. https://doi.org/10.1007/s11154-022-09728-7
- McGinty HL et al. Cognitive functioning in men receiving androgen deprivation therapy for prostate cancer: a systematic review and meta-analysis. Supportive Care in Cancer, 2014. https://doi.org/10.1007/s00520-014-2285-1
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