Testosterone Enanthate and Cognitive Function: What the Evidence Actually Shows

What the evidence actually shows

The Testosterone Trials Cognitive Function Trial enrolled 788 men aged 65 or older with low testosterone and impaired sexual function, physical function, or vitality; 394 received testosterone gel and 394 received placebo gel for 1 year [1]. The results were published in JAMA in 2017 [1]. A subgroup of 493 men met criteria for age-associated memory impairment; their mean age was 72.3 years and mean baseline testosterone was 234 ng/dL [1]. The primary outcome in that subgroup was delayed paragraph recall, a verbal memory test. The trial reported no significant mean change from baseline to 6 and 12 months in that score among men with age-associated memory impairment [1]. It also measured visual memory, executive function and spatial ability [1].

The enanthate-specific human trial is much smaller. In a randomized, double-blind, placebo-controlled study published in Neurology in 2001, 25 healthy community-dwelling men aged 50 to 80 received weekly intramuscular injections of 100 mg testosterone enanthate or saline placebo for 6 weeks [2]. Total testosterone rose an average of 130% at week 3 and 116% at week 6; estradiol rose 77% and 73% [2]. Significant improvements were seen in spatial memory (recall of a walking route), spatial ability (block construction), and verbal memory (recall of a short story) compared with baseline and placebo, although not all measures improved [2]. The authors said it remained unclear whether the improvements came from testosterone, estradiol, or both [2]. The study was small and short, and it enrolled healthy men rather than men with hypogonadism.

Does the formulation change the answer?

The gel trial and the enanthate trial used different formulations and different populations, so their results are not directly interchangeable [1][2].

Testosterone enanthate is an oil-soluble ester of testosterone given by intramuscular injection. The label directs slow, deep injection into the gluteal muscle and the avoidance of intravascular injection [3]. The labeled dose for male hypogonadism is 50 to 400 mg every 2 to 4 weeks; the label says total doses above 400 mg per month are not required and injections more often than every 2 weeks are rarely indicated [3]. Before starting, the label says to confirm hypogonadism with morning serum testosterone measured on at least two separate days and below the normal range [3].

What the label says about safety

Testosterone products are FDA-approved only for men who lack or have low testosterone with an associated medical condition [6]. The May 2026 Hikma testosterone enanthate injection label says safety and efficacy in men with age-related hypogonadism have not been established [3]. FDA requested removal of that limitation in June 2026 [6].

The enanthate label lists polycythemia, stroke, myocardial infarction, depression, anxiety, headache and libido changes as adverse reactions [3]. It says testosterone can increase blood pressure, which can increase cardiovascular risk over time, that blood pressure should be monitored periodically (especially in men with hypertension), and that testosterone products are not recommended in men with uncontrolled hypertension [3]. It also says studies have been inconclusive on major adverse cardiovascular events and that some studies, but not all, have reported an increased risk [3]. For venous thromboembolism, the label says to discontinue treatment if an event is suspected [3].

Polycythemia is an increase in red blood cell mass. A meta-analysis of 19 randomized placebo-controlled trials in men aged 45 or older found hematocrit above 50% was nearly four times as likely with testosterone as with placebo (OR 3.69, 95% CI 1.82 to 7.51); 651 men received testosterone and 433 received placebo [5]. A review notes that short-acting injectable formulations have the highest incidence of erythrocytosis and that the link between erythrocytosis and thromboembolic events remains unclear [7].

What about Alzheimer's disease?

The human data on testosterone and Alzheimer's disease are observational. In the Baltimore Longitudinal Study of Aging, 574 men free of Alzheimer's disease at baseline were followed for a mean of 19.1 years [4]. A higher free testosterone index was associated with lower risk of Alzheimer's disease after adjustment for age, education, smoking status, body mass index, diabetes, any cancer diagnoses and hormone supplements (hazard ratio 0.74 per 10 nmol/nmol increase, 95% CI 0.57 to 0.96), a 26% decrease [4]. Total testosterone and sex hormone-binding globulin were not significant predictors after adjustment [4]. This does not show that testosterone enanthate prevents Alzheimer's disease.

In a triple transgenic mouse model of Alzheimer's disease, gonadectomy increased beta-amyloid accumulation in the hippocampus and amygdala and impaired spontaneous alternation; dihydrotestosterone treatment attenuated both [8]. Animal results do not establish a human treatment effect.

Bottom line

The Endocrine Society guideline recommends diagnosing hypogonadism only in men with symptoms and signs of testosterone deficiency and consistently low morning testosterone [9]. For cognition, the randomized evidence is a 1-year gel trial with no significant change in its primary memory measure [1] and a 6-week enanthate trial in healthy older men with gains on some tests [2].