Key Takeaways
- Total testosterone is the sum of three forms: SHBG-bound (the majority, inactive), albumin-bound (loosely bound and releasable) and free testosterone.
- Free testosterone is only 1 to 3% of the total, yet it is the only form that can activate androgen receptors.
- You can have a normal or even high total testosterone and still feel flat, tired and low in libido if SHBG binds most of it.
- A meaningful panel includes total testosterone, free testosterone, SHBG and albumin, with LH, FSH, prolactin, estradiol, vitamin D, thyroid and fasting insulin adding useful context.
- Before buying any supplement, find out whether your issue is production, signalling, transport, inflammation, sleep or metabolism.
Most men only know one number from their lab report: total testosterone. It is the figure printed in bold, the one most clinics discuss, and the one supplement brands obsess over. But total testosterone alone does not tell you how your hormonal system is performing.
To understand whether testosterone supplements can help, and what kind, we need to start with the most important concept in male endocrine physiology: bioavailability, how much of your testosterone is actually usable by your body. This is why free testosterone is the real marker of androgen function, and why two men with identical total testosterone levels can feel completely different.
Total testosterone: the big number that misleads most men
Total testosterone is the sum of all testosterone circulating in your blood. But it exists in three states:
| Form | How it is held | What it can do |
|---|---|---|
| SHBG-bound (the majority) | Tightly bound | Biologically inactive, cannot enter cells |
| Albumin-bound | Loosely bound | Can be released, counts towards bioavailable testosterone |
| Free testosterone | Not bound to any protein | The only form that can activate androgen receptors |
This means you can have a high total testosterone number while feeling like your system is running in low-power mode, if SHBG is binding most of your testosterone and free testosterone is low.
Free testosterone: the hormone that actually matters
Free testosterone is the portion available for your tissues to use. It drives:
- libido
- morning erections
- muscle protein synthesis
- energy and motivation
- recovery
- red blood cell production (erythropoiesis)
- mood and cognition
If free testosterone is low, your body is not receiving the androgen signal it needs, no matter how high your total testosterone appears on the lab sheet. This is why many men hear "your testosterone numbers look fine" but still feel flat, tired, unfocused, low in libido and below their usual performance. The labs do not match the lived experience because total testosterone does not reflect biological function.
In a study of middle-aged and older men, low free testosterone was associated with hypogonadal signs and symptoms, including in men whose total testosterone was within the normal range. Total testosterone on its own can miss men whose androgen signal is genuinely low.
Antonio L, Wu FCW, et al. "Low free testosterone is associated with hypogonadal signs and symptoms in men." Journal of Clinical Endocrinology and Metabolism. 2016.
A blood test is a snapshot. Your nights are a trend.
Morning erections are on the list of what free testosterone drives. The Adam Sensor tracks your night-time erections every night at home, so between blood tests you can see how your body is actually responding to the changes you make.
Explore the Adam Sensor →What you should measure
To understand your hormonal profile, you need more than total testosterone. A meaningful assessment includes:
- total testosterone
- free testosterone, calculated or measured by equilibrium dialysis
- SHBG
- albumin, for accurate calculations
Optional but insightful: LH (to understand signalling), FSH, prolactin, estradiol, vitamin D, a thyroid panel (TSH and FT4) and fasting insulin (for metabolic assessment). Together these give you a clear view of production, availability, transport, balance, upstream signalling, metabolic constraints and inflammatory stressors.
💡 Key Point
If you only ever see one number, ask for three more. Free testosterone, SHBG and albumin turn "your levels look fine" into an answer that actually explains how you feel.
When to See a Doctor
If your total testosterone came back normal but you still have symptoms such as low libido, fewer morning erections, persistent fatigue or low mood, ask your doctor about measuring free testosterone and SHBG. Testosterone is best tested in the morning, and symptoms like these can have other causes a doctor should rule out.
Why metrics come before supplements
Before you buy a single supplement, you need to know where the problem sits:
- Is it production, or the raw materials for it?
- Is it signalling?
- Is it transport?
- Is it inflammation?
- Is it sleep?
- Is it metabolic?
Understanding total versus free testosterone is the foundation that allows every other part of this series to make sense. If you missed it, start with Part 1: why most testosterone boosters don't work.
Putting it all together
Total testosterone is the big number everyone talks about. Free testosterone is the number that actually matters. This distinction explains why men with normal labs can feel anything but normal, and why supplement strategies must be tailored to your SHBG, your free testosterone, your signalling, your metabolism, your inflammation and your sleep.
This is the first real step towards a targeted, effective testosterone plan. Next, in Part 3: the Adam Health guide, we cover how to put it into practice.
Built to make, free and sustain testosterone
MorningT™ is our 4-in-1 testosterone support system. It supplies the raw materials for production, includes ingredients aimed at freeing testosterone from binding so more is usable, and lists every dose on the label. Three capsules with your first meal.
Sign up for early access →Frequently Asked Questions
What is free testosterone?
Free testosterone is the testosterone in your blood that is not bound to any protein. It is the only form that can activate androgen receptors, which makes it the best marker of how much testosterone your body can actually use.
What percentage of testosterone is free?
Usually only 1 to 3% of total testosterone. Most is tightly bound to SHBG and inactive, and the rest is loosely bound to albumin, from which it can be released.
Why do I feel low when my testosterone is normal?
Total testosterone can look normal while free testosterone is low, if SHBG binds most of it. In that case your body is not receiving the androgen signal it needs, which is why your labs and how you feel don't match.
Which blood tests should I ask for?
Total testosterone, free testosterone (calculated or by equilibrium dialysis), SHBG and albumin as the core. LH, FSH, prolactin, estradiol, vitamin D, a thyroid panel and fasting insulin add useful context about signalling and metabolism.
What is SHBG?
Sex hormone binding globulin is a protein that binds testosterone tightly, keeping it inactive. When SHBG is high, more of your testosterone is locked away and less is free to act on your tissues.
Sources
- Hammond GL. Plasma steroid-binding proteins: primary gatekeepers of steroid hormone action. Journal of Endocrinology. 2016.
- Krakowsky Y, Grober E, et al. Testosterone deficiency: establishing a biochemical definition. Canadian Urological Association Journal. 2017.
- Antonio L, Wu FCW, et al. Low free testosterone is associated with hypogonadal signs and symptoms in men. Journal of Clinical Endocrinology and Metabolism. 2016.
- Dai W, Yeung EH, et al. Determinants of sex hormone-binding globulin in men. Clinical Endocrinology. 2017.
The Adam Health products and services are not medical devices, and are not intended to mitigate, prevent, treat, cure or diagnose any disease or condition. If you have any concerns about your health, please consult your doctor.
Share:
Testosterone Supplements Part 1: Why Most Testosterone Boosters Don’t Work
Testosterone Supplements Part 3: The Adam Health Guide