The bioactive hormone behind energy, libido and performance
Free testosterone is the portion of testosterone in the blood that is not bound to transport proteins and can therefore actually be used in the body. While total testosterone is often measured, it is free testosterone that determines how well your cells can access the hormone.
Many men have normal or slightly reduced total testosterone levels, but low free testosterone . Possible consequences include loss of energy, decreased libido, reduced muscle strength, mental instability, or sleep problems.
What is free testosterone?
Testosterone circulates in the blood in three forms:
- Bound to SHBG (sex hormone-binding globulin) - biologically inactive
- Loosely bound to albumin - potentially bioavailable
- Free (1–3%) - unattached and directly active
Only free testosterone can penetrate target cells, activate receptors, and trigger functions such as libido, muscle building, fat burning, and mental sharpness .
Why is free testosterone so important for men?
Even if total testosterone levels appear normal, a high SHBG level can block the active component . This can explain why men with "normal lab results" can still experience classic symptoms of testosterone deficiency.
- Loss of libido
- Erection problems
- Muscle loss despite training
- Belly fat accumulation
- Irritability, fatigue
- Sleep problems or mental restlessness
Especially men over 35, with a lot of stress or an unbalanced diet, experience a drop in free testosterone - often unnoticed .
How can free testosterone be measured?
It can only be measured directly using specialized laboratory methods (e.g., equilibrium dialysis). More often, it is calculated using the Vermeulen formula, based on:
- Total testosterone
- SHBG
- albumin
Use the free free testosterone calculator to easily calculate your value yourself:
What values are considered normal?
- Free testosterone below 8–10 pmol/L : Common symptoms
- Optimal range for men: 10–25 pmol/L , depending on age and activity level
- Important: Laboratory reference ranges are often too broad and "downplay" true deficiencies.
Free testosterone below your personal optimal range can already lead to significant limitations, even if your total testosterone is still normal.
What influences the free testosterone level?
Increased SHBG:
- Liver diseases
- Overtraining
- Calorie deficit / Underweight
- Excessive alcohol consumption
- Hyperthyroidism
- Stress hormones such as cortisol
Low total testosterone:
- Old
- Overweight
- Lack of sleep
- Inflammation (indication e.g. by elevated CRP)
- Hormonal imbalance
Therefore, it is crucial not only to measure total testosterone , but also to calculate or specifically determine free testosterone.
How can you improve free testosterone levels?
1. Lower SHBG (in case of excessively high levels):
- A balanced diet with sufficient protein intake
- Avoiding extreme calorie deficits
- Stress and cortisol reduction
- Thyroid optimization (check fT3, fT4)
- Zinc, boron and magnesium as SHBG-modulating minerals
2. Increase total testosterone:
- Strength training & interval training
- Healthy sleep (in a dark, cool sleeping environment)
- Sufficient healthy fats (e.g., Omega-3, avocado, eggs)
- Optimize micronutrients, vitamins and supplements such as zinc, vitamin D, DHEA, ashwagandha (under medical advice)
- Testosterone replacement therapy (TRT) - in cases of proven deficiency
Do you want to know your exact status?
Laboratory testing is available at your family doctor's office, at specialists' offices, or at direct laboratories. With the TRT-Check from Adon Health, you can also get an initial overview of your free testosterone and other relevant lab values for your hormone balance – conveniently from home.
👉 Order your test kit now - TRT Check at Adon Health
Conclusion
Free testosterone is the "real" active ingredient behind your hormone levels. It determines how powerful, focused, sexually active, and resilient you are. Many men suffer from symptoms even though their overall levels are "normal" because their free testosterone is too low.
Tip: Read our blog post on understanding testosterone levels or listen to the podcast episode with Dr. Andreas Scholz , in which the real values of Dr. Jonathan Apasu are evaluated.
