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Testosterone is the best-known androgen (male hormone), but females produce it too. In both sexes, low testosterone can reduce libido and cause fat gain, muscle loss, and bone loss.

Our evidence-based analysis on testosterone features 182 unique references to scientific papers.

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Summary of Testosterone

Overview | How are testosterone levels assessed? | What affects testosterone?


Testosterone is a hormone produced primarily in the testes in men and the ovaries in women. Testosterone is connected to sexual development, muscle building, fat loss, some aspects of cognition, and hair loss.[1]

Your testosterone levels may not tell the whole story of how testosterone is functioning in your body. Total testosterone can be divided into three categories.[2]

  • Tightly bound testosterone: About two-thirds of the testosterone in your blood is bound to sex hormone binding globulin (SHBG). It is not readily available for use by your body.

  • Loosely bound testosterone: About one-third of the testosterone in your blood is weakly bound to albumin. Once the bond is broken, the testosterone circulates as free testosterone in your body.

  • Free testosterone: A small percentage of the testosterone in your blood (1–4%, as a rule) floats around freely. Your body can readily use it, and the enzyme 5-alpha-reductase can convert it to dihydrotestosterone (DHT), a very potent androgen.

Together, your loosely bound and free testosterone compose your bioavailable testosterone, which has a greater impact on your health than your total testosterone.

How are testosterone levels assessed?

A blood test is used to assess testosterone and its components (free T, bound T, etc). Abnormally low or high levels can cause health issues in males and females.

When your T levels are tested, the reference range can vary a lot from lab to lab. A recent study showed that the bottom of the range for males can be 5.55–10.4 nanomoles per liter, or nmol/L (160–300 nanograms per deciliter, or ng/dL), and the top of the range can be 25.17–39.18 nmol/L (726–1,130 ng/dL).[3] So if you get measured at 280 ng/dL, you may or may not be considered as having “low testosterone”.[3]

Because testosterone levels can fluctuate throughout the day, the test should be performed in the morning (8–11 a.m.). If the results come back low, a second test can be ordered to confirm the first result. As part of the workup, your physician may also measure your levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and the T4 thyroid hormone (thyroxine) to get an accurate diagnosis.

Assessing testosterone levels

What are the symptoms of abnormal testosterone levels?

The symptoms vary between males and females. The table below lists the more common manifestations.

Symptoms of abnormal T levels in males

Delayed puberty

Congenital adrenal hyperplasia


High blood pressure

Erectile dysfunction

High heart rate

Excess breast tissue (gynecomastia)

Possible tumor in the adrenal glands

Hair loss

Possible tumor in the testicles

Increased body fat

Issues with fertility

Issues with pituitary gland

Loss of muscle mass

Low libido / sex drive

Low sperm count

Poor bone health

Stunted growth

Symptoms of abnormal T levels in females

Addison’s disease

Abnormalities with menstrual periods



Issues with fertility

Congenital adrenal hyperplasia

Excess body and facial hair

Increased muscle mass

Polycystic ovary syndrome (PCOS)

Possible tumor in the adrenal glands

Possible tumor in the ovaries

Voice deepening

Weight gain

What affects testosterone?


Try to get enough vitamin D, zinc, and magnesium in your diet, as these are key nutrients for supporting healthy testosterone levels. However, if dietary changes prove insufficient, supplementation can help make up the difference.

But supplements can’t replace a healthy lifestyle. To optimize your testosterone production, make sure you get enough quality sleep, incorporate some resistance training into your workout program, and monitor your weight.

The table below displays an analysis of human studies and indicates how supplements may affect testosterone.

If you are looking for a complete, precise, step-by-step guide on supplementing for optimal testosterone production, we recommend you look at our Testosterone Supplement Guide.

It’s based on science, not marketing hype. Best of all, it comes with free lifetime updates (and is backed by an unconditional 100% money back guarantee).


Lack of sleep can notably decrease testosterone production[4][5][6][7][8] and facilitate fat gain[9] (which itself can impair testosterone production).

Weight management

Fat gain and its associated chronic diseases, such as cardiovascular disease and type 2 diabetes,[10][11][12] are strongly linked to decreases in testosterone, particularly in middle-aged and older men.

If you gain weight — fat, not muscle — your testosterone production can drop. Fortunately, if you lose fat, your testosterone production can climb back up.

Both observational studies[10] and randomized controlled trials (RCTs)[13] have shown consistent results: in males who carry excess fat tissue, the greater the weight loss, the greater the testosterone increase.

A meta-analysis of 24 RCTs looked at weight loss as a result of diet or bariatric surgery in males.[13] In the diet studies, the average 9.8% weight loss was linked to a testosterone increase of 2.9 nmol/L (84 ng/dL). In the bariatric-surgery studies, the average 32% weight loss was linked to a testosterone increase of 8.7 nmol/L (251 ng/dL).

You don’t need to lose huge amounts of weight to see a bump in your testosterone levels either. Males that reduce weight by just 5% can increase total testosterone by 2 nmol/L (58 ng/dL).[14]


Resistance training can raise testosterone levels for 15–30 minutes after exercise.[15][16] More important, it can benefit testosterone production in the long run by improving body composition and reducing insulin resistance.[15]

Overtraining, however, is counterproductive. Prolonged endurance training especially can cause your testosterone to drop.[17][18] Ensuring adequate exercise recovery time will help you reap the full benefits of physical activity.


Middle-aged[19] and older[20] males see their total testosterone levels decrease by 0.4% to 1.6% per year, many of whom had lower-than-average levels even in their 30s.[21] Bioavailable testosterone decreases by about 2–3% a year.[19] 

Those numbers can be pretty misleading though. Men approaching middle age tend to exercise a lot less and eat a lot worse. So it’s hard to say what a “natural” decline in testosterone looks like on a population-wide basis.

It’s kind of like saying muscle mass decreases 1–2% a year once you hit middle age. That decrease can have a lot to do with more time spent on work and family and less time spent trying to get ripped.

Medical conditions

Hypogonadism, when the body’s sex glands (testes, ovaries) underproduce hormones, is a prominent cause of abnormal testosterone levels. There are many potential causes of hypogonadism.

A deficiency in the enzyme 5-alpha-reductase, which converts testosterone to the more active dihydrotestosterone (DHT) form, will present as low T levels and/or abnormal genitalia formation at birth due to the lack of DHT.

In females, polycystic ovary syndrome (PCOS) can elevate levels of androgen hormones, including testosterone (T), free testosterone, dehydroepiandrosterone (DHEA), and DHEA sulfate (DHEAS).[22] These elevated levels can cause body-hair growth, acne flare-ups, and a type of hair loss more consistent with male-pattern hair loss than female-pattern hair loss.



Testosterone replacement therapy (TRT) is a prescription testosterone treatment for increasing T levels. It’s commonly used for males with low T and transgender males, but may also be used for primary hypogonadism, metastatic breast cancer, delayed puberty, and hypogonadotropic hypogonadism.

TRT can be delivered in a variety of ways.

  • Buccal tablet (dissolves in the mouth)

  • Injection into the muscle or subcutaneous tissue

  • Nasal gel

  • Oral capsule

  • Subcutaneous implant

  • Topical gel or solution

  • Transdermal patch (worn on the skin)

TRT may cause side effects and increase certain health risk factors, which should be monitored by your physician.

Side effects and risks of TRT


Blood clots

Heart attack risk

Back pain

Difficulty breathing, especially during sleep

Prostate cancer risk

Breast enlargement or pain

Enlarged prostate, leading to difficulty urinating

Stroke risk


Erections that last too long

Headaches or migraine

Erections that occur too frequently

Increased cholesterol

Large mood changes, including depression, anxiety, or suicidal thoughts

Issues with fertility

Lower leg pain, swelling, warmth, or redness

Injection site irritation
(pain, redness, bruising, bleeding, or hardness)

Nausea or vomiting

Joint pain

Pain in the upper right part of the stomach

Moderate mood swings

Problems with urination
(difficulty; weak flow; frequent, sudden need to go immediately; blood in the urine)

Sleep problems

Swelling of the hands, feet, ankles, or lower legs

Voice deepening

Worsening heart failure

Voice hoarseness

Yellowing of skin or eyes

Weight gain

Drugs that inhibit CYP19A1, the aromatase enzyme, are indirect testosterone boosters in males. CYP19A1 serves many purposes, one of which is to convert testosterone to estradiol, the predominant form of estrogen. Inhibiting this enzyme reduces the percentage of testosterone that gets converted to estradiol.

It may seem counterintuitive, but the male body needs estradiol,[23] though in a lesser quantity than females need. When the body detects that estradiol levels are too low, it reacts by increasing its production of the base material it needs to make estradiol: testosterone.


Several drugs and drug classes may decrease testosterone levels. If you are on any of the medications below and are concerned about your T levels, consult your physician. Do not stop the treatment without professional medical input.

  • Antiandrogens (e.g., cyproterone, bicalutamide, flutamide, spironolactone)

  • Chemotherapy (e.g., alkylating agents)

  • Chronic anabolic steroid use (particularly when high doses are used)

  • Glucocorticoids

  • Ketoconazole

  • Luteinizing hormone-releasing hormone agonists (aka LHRH analogs or GnRH agonists)

  • Opioids

  • Radiation therapy (total body or pelvis in particular)

  • Selective serotonin reuptake inhibitors (SSRIs)

  • Suramin

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Human Effect Matrix

Unlocked for Examine members

The Human Effect Matrix looks at human studies to tell you what supplements affect Testosterone.

Full details on all Testosterone supplements are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Supplement Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-a Notable High See all 18 studies
There appears to be an increase in testosterone following DHEA supplementation, but the vast majority of literature is in menopausal women (where testosterone contributes to libido). There is variability in the results, and DHEA is unreliable in increasing testosterone, but this unreliability extends to all demographics and subjects (with limited evidence of DHEA increasing testosterone in all studies including youthful athletes, which are less studied).
- See all 9 studies
There appears to be a time-dependent influence on testosterone, with acute doses of alcohol increasing testosterone secondary to creating energy influx in the liver (small enough of an increase to be 'somewhat' effective but may contribute to libido) whereas abuse is known to reduce testosterone levels more notably. The acute increase in testosterone is thought to be related to spikes in libido
grade-b Minor Very High See all 7 studies
Testosterone may be increased in infertile men (who have a reduction in testosterone) and men undergoing strength training, but there is currently no evidence to suggest an inherent testosterone boosting effect in otherwise normal men.

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Frequently Asked Questions and Articles on Testosterone

How can you increase testosterone naturally?
When it comes to increasing your testosterone, quality sleep, physical activity, and weight management come first. A few supplements can help sustain healthy testosterone levels, but most supplements marketed as testosterone boosters don’t work, though some can make you believe they do by boosting your libido.
Does creatine cause hair loss?
It’s plausible, but unlikely. One RCT linked creatine supplementation to an increase in DHT — an androgen involved in hair loss — but this RCT has never been replicated.
How important is sleep?
Sleep is incredibly important, and can be considered crucial alongside diet and exercise. Proper sleep habits help sustain many biological processes, and bad sleep can cause these processes to be suboptimal or even malfunction.
Does ashwagandha increase testosterone?
There is a bit of evidence that shows Ashwagandha increases testosterone, but it is not convincing.
Can creatine increase your testosterone levels?
There is no convincing evidence that creatine can increase your testosterone levels.
Do herbal aphrodisiacs work?
It depends on the product touted to be an aphrodisiac, but some of them do apparently increase sexual desire; it is a relatively under-researched topic though, and we don't know why they increase sexuality.
Four Testosterone Boosters and Sketchy Research
Is semen high in protein?
Yes. Semen is 50% protein by weight and contains a variety of nutrients to protect the sperm cells from damages.
Does ejaculation affect testosterone levels?
Ejaculation results in changes in prolactin (increase) and dopamine (temporary decrease), but does not result in changes in testosterone. Although prolactin and dopamine are both involved with testosterone, they do not appear to influence testosterone levels acutely.
What is 'roid rage'?
Mostly a myth; testosterone (including injections) can increase impulsivity in some but this does not appear to be reliable (does not affect every person tested), impulsivity might lead to aggression but this is drawing at straws now with the connections

Things to Note

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