Testosterone Therapy for Men and Women: A Complete Guide

Testosterone is the hormone most people associate exclusively with men. That’s the first misunderstanding I try to correct in the clinic. Women produce testosterone too — in the ovaries and adrenal glands — and its decline in both sexes is one of the most clinically significant and consistently underdiagnosed aspects of aging.

Over the years I’ve consolidated five areas where testosterone has clear, evidence-based effects: cardiovascular health, body composition, libido and sexual function, cognitive performance, and bone structure. This article covers all of them, plus how I approach testing and when therapy is appropriate versus when lifestyle and supplements come first.

What testosterone actually does — in men and in women

In men, testosterone is produced primarily in the testicles and accounts for about 85% of total circulating androgen. It drives muscle protein synthesis, bone density maintenance, red blood cell production, sperm maturation, and libido. Levels begin declining at approximately 1% per year after age 30 — slow enough to go unnoticed for years, significant enough to accumulate into a clinical picture by the mid-40s or 50s.

In women, testosterone circulates at roughly 5–10% of male levels, but its effects are proportionally important. Low testosterone in women contributes to low libido, reduced muscle tone, fatigue, mood instability, and cognitive fog. The drop during perimenopause and menopause is often sharper than the decline in estrogen — yet hormone workups frequently stop at estradiol and progesterone, leaving free testosterone unmeasured.

Beyond sexual function, testosterone plays roles that are rarely discussed in routine care:

• Muscle mass: Testosterone allows muscles to develop faster and maintain their anabolic state. This matters not just for performance but for metabolic health — lean mass determines how efficiently you burn energy at rest.
• Bone formation: The hormone is directly involved in maintaining bone density and stimulating bone marrow space. Deficiency is a meaningful contributor to osteoporosis in both sexes.
• Fertility: In men, testosterone is essential for the formation and maturation of spermatozoa in the testicles. Low levels reduce semen density and quality. In women, testosterone influences embryonic development and sexual organ sensitivity.
• Energy and mood: Testosterone maintains normal pineal gland signalling, which affects circadian rhythms, energy regulation, and psychological resilience. The flat affect and persistent low energy common in andropause are often misattributed to depression.

Cardiovascular benefits: what the evidence shows

The cardiovascular picture for testosterone is one I find underappreciated — and historically misrepresented. When levels are brought into physiological range, the effects on the heart and vasculature are largely beneficial.

HDL cholesterol and lipid balance

Low testosterone is associated with reduced HDL (good cholesterol). Restoring it to normal levels stimulates lipoprotein production, which improves the coronary artery environment and reduces the lipid burden that contributes to atherosclerosis. Testosterone also reduces LDL and triglycerides in testosterone-deficient men.

Blood pressure and nitric oxide

Testosterone has a direct pharmacological effect on nitric oxide — the molecule that keeps blood vessels relaxed and blood pressure in its normal range. It is also the same pathway relevant to erectile function. Men with chronically high blood pressure frequently have low testosterone, and correcting the deficiency helps control the vascular dilation and arterial wall thickening that drive hypertension.

Insulin sensitivity and diabetes risk

Testosterone causes the body to respond more efficiently to insulin. When testosterone is deficient, insulin sensitivity falls — which raises blood sugar, promotes visceral fat accumulation, and increases coronary artery disease risk. This is why I consider testosterone alongside glucose and insulin when evaluating metabolic health. The two are directly linked.

Cardiac muscle structure

The heart is a muscle, and testosterone plays a role in its protein synthesis and structural maintenance. Low testosterone is associated with reduced cardiac output and insufficient muscular adaptation. Raising levels to normal helps balance blood flow and maintain the muscular architecture of the heart.

Clinical note: A review of blood testosterone volume can directly guide the appropriate supply needed to maintain optimal cardiovascular health. The risks associated with testosterone in older studies mostly involved supraphysiological doses — not properly managed physiological replacement.

DHT and libido: the conversion most people don’t know about

Testosterone doesn’t act on libido directly in its original form. It undergoes enzymatic conversion — via 5-alpha reductase — to dihydrotestosterone (DHT), which is the primary androgenic driver of sexual desire. This conversion occurs in the prostate, adrenal glands, testes, and hair follicles.

DHT is considerably more potent than testosterone at androgen receptors. Experimental studies showing castrated animals recovering libido after DHT (not testosterone) injections confirmed its primary role. The same principle applies clinically: patients who report low libido despite adequate total testosterone often have impaired DHT conversion, which requires a different assessment and intervention approach than total testosterone deficiency alone.

DHT also influences adrenal function — it plays a role in adrenaline release, which in turn raises metabolic activity. When energy increases, libido follows. This is one reason why fatigue and low libido tend to track together, and why restoring testosterone alone is sometimes insufficient if DHT levels remain low.

Normal DHT range: 40–575 ng/dL. Below 40 ng/dL, patients typically report lethargy, fatigue, and reduced sexual motivation. Testing DHT alongside free testosterone gives a more complete picture of androgen status than total testosterone alone.

Free vs.

total testosterone: why the standard lab panel often misses the problem

This is the distinction I raise most often with patients who arrive having been told their testosterone is “normal.” Total testosterone measures all testosterone in the blood — including the fraction bound to sex hormone-binding globulin (SHBG) and albumin, which is biologically inactive. Free testosterone is the small fraction not bound to any carrier protein, and it is the only fraction your cells can actually use.

A patient can have a total testosterone result in the normal reference range while free testosterone is significantly low — because SHBG is elevated, locking up most of the circulating hormone. This is particularly common in men over 50 and in women during perimenopause, when SHBG levels tend to rise.

When I hear things like: “I sleep but never feel rested”, “My focus and motivation are gone”, or “Workouts feel harder than they should” — I always order free and total testosterone, SHBG, estradiol, and DHT together. Even mild deficiencies in free testosterone can affect daily function, and they often go undetected if only total testosterone is measured.

The practical takeaway: if your lab says normal but you still feel off, the number reported is probably not the number that matters. Tools like Optimal Blood flag exactly this problem — they compare your free testosterone against functional ranges, not just the standard reference interval.

Testosterone and body composition: the weight loss connection

The relationship between testosterone and body fat is bidirectional. Low testosterone promotes fat accumulation, particularly visceral fat — and excess visceral fat, in turn, increases aromatase activity (the enzyme that converts testosterone to estradiol), further lowering testosterone. It becomes a self-reinforcing cycle.

Restoring testosterone interrupts this cycle through two mechanisms: it increases lean body mass (which raises basal metabolic rate) and it improves insulin sensitivity (which reduces the metabolic drivers of fat storage).

Five-year clinical data: In a study of 115 testosterone-deficient men with a mean age of 61, hormone replacement over five years produced an average weight loss of 16 kg and reduced mean waist circumference from 107 cm to 98 cm. Blood pressure and metabolic profiles also improved progressively over the study period. The improvements were not front-loaded — they accumulated continuously across five years, which reflects the nature of hormonal optimization as a long-term process rather than an acute intervention. (Presented at the European Congress on Obesity, Lyon.)

Increased testosterone also improves energy and motivation for physical activity — a factor that’s hard to quantify but clinically real. Patients who felt too tired to exercise consistently report returning to training within weeks of normalizing their levels, which compounds the body composition benefits.

Natural approaches before considering therapy

Not every patient with suboptimal testosterone needs pharmaceutical intervention. Before recommending therapy, I look at what can be addressed through diet, supplementation, and training.

The natural mechanisms for supporting testosterone production include:

• Resistance training: Particularly compound lifts targeting the large gluteal and thigh muscles, which have the highest concentration of androgen receptors and the greatest hormonal response to mechanical load.
• Adequate caloric intake: Chronic caloric restriction suppresses testosterone. Maintaining a sufficient baseline (approximately 2,500 kcal for active men) keeps the hypothalamic-pituitary-gonadal axis from entering a conservation state.
• Zinc: An essential cofactor in testosterone synthesis. Deficiency is common, particularly in patients who sweat heavily, eat limited meat, or take proton pump inhibitors (which reduce mineral absorption).
• Vitamin D: Functions as a steroid hormone precursor. Vitamin D receptors are present in testicular Leydig cells, the primary site of testosterone production. Deficiency is a correctable contributor to low testosterone in a significant portion of patients.
• Niacinamide (Vitamin B3): Supports DHT production and overall androgen metabolism.
• Sleep: The majority of daily testosterone is produced during deep sleep. Poor sleep architecture — fragmented sleep, insufficient slow-wave sleep — meaningfully suppresses production independent of all other factors.

If these are optimized and levels remain low with persistent symptoms, therapy is the appropriate next step. The key is always testing first, then deciding — never the reverse.

When to consider testosterone therapy

The decision follows a structured assessment, not a symptom checklist alone. What I look for before recommending therapy:

• Free testosterone clearly below optimal range (not just below the bottom of a wide reference interval)
• SHBG elevated, explaining the gap between total and free levels
• Symptoms that are functional — affecting work performance, physical capacity, sleep quality, or sexual health — not just mild background complaints
• Natural and lifestyle approaches already optimised (sleep, training, nutrition, zinc/D3 repletion)
• No contraindications (prostate-specific antigen evaluation in men over 45, cardiovascular risk stratification)

When those criteria are met, bioidentical testosterone — dosed and monitored with follow-up testing at 6–8 weeks — typically produces measurable and sustained improvement. The form of delivery (gel, cream, or intramuscular) depends on individual absorption profiles, which vary considerably. Some patients absorb transdermal preparations poorly despite adequate dosing — a separate clinical problem addressed by route adjustment rather than dose escalation.

The goal of therapy is not to maximise testosterone. It is to restore it to the range where the body functions as it was designed to — and then verify that result with blood work, not just symptom reporting.

Sources: European Congress on Obesity, Lyon — testosterone replacement & body composition (5-year study, n=115) · LiveScience: Testosterone overview · DHT and libido — experimental androgen studies (5-alpha reductase pathway) · Free testosterone and SHBG — standard clinical endocrinology reference