Key takeaways
- LH and FSH read alongside testosterone decide the pathway before testosterone does.
- High LH with low testosterone is primary hypogonadism, where replacement is the correct treatment.
- Low or normal LH with low testosterone is a signalling problem with a cause, usually fat, sleep, alcohol, opioids or a previous cycle.
- Enclomiphene raises the body's own signal and preserves fertility, which fits secondary hypogonadism better than replacement does.
- Retest at three to six months, not six weeks, because a shorter interval mostly measures noise.
A 26-year-old with a low testosterone reading, poor sleep, thirty pounds of extra weight and a stressful job does have low testosterone. What he usually does not have is a testicular or pituitary disease. Those two facts point in completely different directions, and the direction picked at that first appointment tends to be the one he is still on ten years later. Starting in your twenties usually means staying on, so the sequence of decisions matters more here than in almost any other age group.
Why low testosterone is rising in young men
Population data show men's testosterone has fallen roughly 20% over thirty years, independent of age — a man of a given age today measures lower than a man of the same age decades earlier (Travison et al., J Clin Endocrinol Metab 2007). A decline of that shape over that timescale is not a change in human genetics. It is a change in the conditions the endocrine system is operating in.
- Rising obesity — visceral fat aromatises testosterone to estradiol and lowers SHBG, and that estradiol feeds back on the hypothalamus to cut LH output
- Sleep deprivation — one week of restricted sleep measurably lowers daytime testosterone in healthy young men (Leproult & Van Cauter, JAMA 2011)
- Chronic stress — sustained cortisol signalling suppresses the axis at the hypothalamus
- Sedentary living, low sunlight, higher alcohol intake, frequent cannabis use
- Chronic opioid prescriptions, which suppress testosterone reliably and often severely (Daniell, J Pain 2002)
- Environmental endocrine-disrupting compounds
Almost every item on that list is upstream of the testes rather than in them. That is the whole reason the sequence below exists.
The distinction that decides everything: primary or secondary
The most useful thing on a young man's panel is not testosterone. It is LH and FSH read alongside it.
In primary hypogonadism the testes cannot produce enough testosterone. The pituitary notices and shouts louder, so LH and FSH run high while testosterone stays low. Nothing upstream will fix this, because the signal is already maximal. Replacement is the treatment.
In secondary hypogonadism the testes are capable but under-instructed. LH and FSH are low or inappropriately normal — normal alongside a low testosterone is itself abnormal, because it should have risen. The problem is the signal, and the signal has causes: fat mass, sleep, opioids, alcohol, stress, prolactin, prior anabolic steroid exposure. Most young men are in this group.
Treating secondary hypogonadism with exogenous testosterone without asking why the signal was low replaces a suppressed axis with a shut-down one, and closes off the options that would have restored natural production.
Reversible causes to address first
Before considering testosterone therapy in a man under 30, the workup should rule in or out:
- Obesity and metabolic syndrome — the most common reversible driver, and one that improves with partial weight loss rather than requiring it to be complete (Rastrelli et al., functional hypogonadism and weight loss)
- Obstructive sleep apnoea, screened with a home study where there is snoring or unexplained daytime fatigue
- Vitamin D deficiency, chronic stress and poor sleep hygiene
- Alcohol above roughly seven drinks a week; opioid medication, including long-standing low-dose use
- Prior anabolic steroid or SARM use — suppression can persist for months to years, and recovery is often possible with time (steroid-induced hypogonadism and axis recovery)
- Hyperprolactinaemia, haemochromatosis, coeliac disease and other systemic illness
The workup
A young man with suspected low testosterone deserves a full picture on the first draw, taken in the morning and confirmed on a second occasion. Free testosterone matters more than usual here, because high SHBG can leave the total looking fine when the free is not, and obesity does the reverse — free versus total testosterone covers why they diverge.
- Total and free testosterone (calculated), SHBG
- LH and FSH — the primary-versus-secondary question
- Sensitive estradiol
- Prolactin
- Full thyroid: TSH, free T3, free T4
- Fasting insulin, HbA1c
- Liver and iron panel, including ferritin and transferrin saturation
- Vitamin D, B12
- Sleep study if there is any suggestion of apnoea
- Pituitary MRI if prolactin is elevated or there are visual or headache symptoms
First-line interventions, and what to expect
For a young man with low testosterone and reversible drivers, the first pass is unglamorous and works more often than people expect:
- Sleep — seven to nine hours, and treat apnoea if present
- Lose visceral fat, by whatever route is realistic and medically appropriate
- Eat enough — chronic under-eating suppresses the axis independently of body fat
- Resistance training three to four days a week, and reduce alcohol
- Address chronic stress directly, and correct any frank nutrient deficiency
- Retest at three to six months
What to expect: sleep changes show fastest, within weeks. Weight-driven changes track the fat loss and take months, largest in men with the most visceral fat to lose. Axis recovery after anabolic steroid use is slowest, measured in seasons. A retest at six weeks mostly measures noise; three to six months is the honest interval. Raising testosterone naturally and sleep and testosterone cover the individual levers.
Why enclomiphene often fits better here
Enclomiphene blocks estrogen feedback at the hypothalamus. With that brake released, LH and FSH rise and the testes produce more of their own testosterone (Wiehle et al., Fertil Steril 2014). For secondary hypogonadism that is a mechanistic match — the problem was the signal, and this raises the signal.
The advantages follow from the mechanism: the axis stays intact, fertility is maintained or improved rather than reduced, and stopping is straightforward because there is no exogenous hormone to come off. So do the limits — it does nothing in primary hypogonadism, the effect size is generally smaller than replacement, and a minority report visual disturbance that warrants stopping. Enclomiphene versus TRT compares them directly.
When testosterone therapy is the right answer under 30
- Documented primary hypogonadism — testicular failure, with high LH and FSH
- Klinefelter syndrome or another genetic cause
- Post-chemotherapy, post-radiation, or established pituitary disease
- Long-term opioid therapy that cannot be discontinued
- A failed enclomiphene trial after reversible causes were genuinely addressed
- Completed family planning, persistent symptoms, and an informed decision to accept lifelong therapy
None of those is unusual, and a young man who meets one should not be made to feel suspect for treating it.
Fertility, which is the part that gets decided by default
Exogenous testosterone suppresses LH and FSH, and without FSH sperm production falls — often to zero. In a 26-year-old this is rarely discussed with the seriousness it deserves, because the consequence arrives years after the decision. Options, in rough order:
- Enclomiphene first, which raises testosterone without suppressing spermatogenesis
- HCG alongside testosterone, maintaining intratesticular testosterone — see fertility on TRT and HCG alongside TRT
- Sperm banking before starting, cheap relative to the alternative
- Deferring treatment until family planning is complete, where symptoms allow
Recovery after stopping is usual but not guaranteed, and takes months to more than a year. That uncertainty is the argument for deciding deliberately rather than discovering it later.
The clinical pearl: in a man under 30, LH and FSH decide the pathway before testosterone does. High LH with low testosterone is a testicular problem, and replacement is appropriate. Low or normal LH with low testosterone is a signalling problem with a cause — usually fat, sleep, alcohol, opioids or a previous cycle. Treat the cause, then the signal, then consider replacement.
Bottom line
TRT in men under 30 is not wrong, and for documented primary hypogonadism it is the correct treatment. It is, however, routinely used first in a group where it should be used last. Most young men with low testosterone have low LH alongside it and a reversible driver behind that — visceral fat, poor sleep, alcohol, opioids, chronic stress, or a suppressed axis after a cycle. Address those, retest at three to six months rather than six weeks, consider enclomiphene where the axis is intact and fertility matters, and reserve replacement for the cases that need it. Starting in your twenties usually means staying on for life: a fine decision to make deliberately, a poor one to arrive at by default. The 60-second assessment is where a physician review of a full panel starts.
Educational content, not medical advice. Laboratory interpretation and any treatment decision are made by a licensed physician after individual evaluation. Individual results vary.
