Why Is My Testosterone Low, and What Comes Next?

If your testosterone came back low, it's natural to ask whether treatment is the next step.

It might be. Investigating the cause doesn't mean treatment is off the table or that you're being told to endlessly "wait and see."

But jumping straight to a prescription before asking why is where care breaks down. Understanding the cause helps decide what can be improved, whether treatment for low testosterone belongs alongside that work, and which options fit your health and fertility goals.

Low testosterone is almost always the result of something else, and for most men that something isn't a rare disease. It's something common, like excess weight and the insulin resistance that travels with it, or untreated sleep apnea, and those causes can often be improved. Rarer causes exist too, and a good workup is built to catch them without putting every man through every test.

How Your Body Makes Testosterone

Testosterone is made in your testes, but the order to make it starts in your brain. A region at the base of the brain called the hypothalamus sends out a hormone in steady pulses, which prompts the pituitary gland just below it to release two more: LH and FSH.

LH travels through your bloodstream to the testes and tells them to make testosterone. FSH works alongside the testosterone made inside the testes to keep sperm production going. Doctors call this chain the HPG axis, short for hypothalamus, pituitary and gonads. [1,2]

The system regulates itself. Your brain keeps track of how much testosterone is circulating, and when levels rise it eases off the signal, much like a thermostat turning down the heat once a room is warm. When levels fall, it pushes harder.

That feedback loop is what makes LH so useful. When your testosterone is low, your LH shows which side of the system is failing:

• High LH (A Testes Problem): Your brain is sending a strong signal, and your testes aren't able to respond to it. Doctors call this primary hypogonadism, and turning up the brain's signal won't help.
• Low or Normal LH (A Signal Problem): The signal itself is weak. A healthy brain would be pushing harder. Doctors call this secondary hypogonadism. [1,2]

When the testes are the problem, LH doesn't always rise as much as you'd expect, which is where FSH comes in. It's a more advanced read, but FSH often climbs even when LH lags, so a high FSH helps confirm that your brain really is shouting at your testes. [1,2]

The most common causes of low testosterone, excess weight and insulin resistance, along with sleep apnea to a lesser extent, act on the signal side. The machinery is usually intact, which is why these causes are so often reversible.

Prolactin

Prolactin is the third hormone worth checking at this stage. It's also made by the pituitary, and when it runs high it quiets the brain's signal, lowering testosterone and often libido along with it. The usual culprits are certain medications and a benign pituitary growth called a prolactinoma, which typically responds well to medication. That's why prolactin belongs alongside LH and FSH whenever the signal looks weak. [1]

Why This Matters for Fertility

The same feedback loop explains why testosterone therapy affects fertility. When testosterone comes from outside your body, your brain sees plenty in circulation and turns down LH and FSH. Your blood level goes up, but the testosterone inside your testes falls along with the signal. That level normally runs many times higher than the level in your blood, and sperm production depends on it. [3]

The feedback loop also explains how the medications that raise testosterone while protecting fertility work:

• hCG mimics LH and acts directly on the testes.
• Clomiphene and enclomiphene block the brain from sensing estrogen, a hormone your body makes partly from testosterone. The brain reads that as a drop in levels and sends a stronger signal. Enclomiphene is a refined and more selective version of clomiphene.

All of them depend on testes that can still respond, so they only make sense when the problem sits on the signal side. [3]

Insulin Resistance: The Most Common Cause

Excess weight and metabolic dysfunction are the most common drivers of low testosterone. Insulin resistance is the common thread running through excess weight, metabolic syndrome, type 2 diabetes and fatty liver, and it pulls testosterone down in two ways:

• It lowers SHBG. That pulls your total testosterone down even when your free testosterone holds up, the "false alarm" covered in Understanding Your Testosterone Results.
• It quiets the signal from the brain. In a study of men with type 2 diabetes, a third had low free testosterone measured by equilibrium dialysis, and their LH and FSH were lower than in men with normal levels, which points squarely at the signal side. [4]

Fatty liver is part of the same picture. Across studies of more than 13,000 men, those with fatty liver had consistently lower testosterone. [5]

The good news is that this is the cause most likely to improve. When researchers pooled diet and bariatric surgery studies, total testosterone rose by roughly 80 ng/dL on average after a low-calorie diet and by roughly 250 ng/dL after bariatric surgery, with LH and FSH rising along with it. How much weight a man lost was the best predictor of how much his testosterone rose. [6] Checking for insulin resistance is straightforward, since an A1c, fasting labs and liver enzymes tell most of the story.

GLP-1 medications appear to work through the same route. Studies in men with metabolic problems have found higher total testosterone with these medications, without suppressing LH and FSH. [7] In a 16-week trial comparing liraglutide with testosterone therapy in men with obesity-related low testosterone, liraglutide raised LH and FSH, keeping the body's own production running, while testosterone therapy shut that signal down. [8]

This is also where care too often stalls. You hear "lose weight and we'll recheck," and then you wait. The advice isn't wrong, but "lose weight" with no support, no goal and no date to reassess isn't a treatment plan. It's a way to end the visit.

Sleep Apnea

Sleep apnea often travels with excess weight, and it's the other common cause worth ruling out. Its link with low testosterone is clearest when the apnea is severe. [9] Loud snoring, waking up unrefreshed and daytime sleepiness are the usual clues, and a sleep study, often done at home, confirms it.

It's also a trap. Men are told "use your CPAP, see you in six months," and the testosterone question gets parked. Across trials, CPAP hasn't reliably raised testosterone, even in men who started out low. [10] One recent study did find testosterone improved on CPAP in men with severe obesity and severe apnea, so it can help some men, but that's no reason to put everything else on hold. [11] Treat the apnea, because it matters for your health. Just don't let it become your testosterone plan.

Less Common Causes

A handful of other causes are worth ruling out, even though they explain far fewer cases.

• Iron overload: Most often from an inherited condition called hemochromatosis, iron can build up in the pituitary and quiet the signal to the testes. It rarely announces itself early, but iron studies (ferritin and transferrin saturation) catch it easily, which is why they belong in the workup whenever the signal looks weak. [1]
• Zinc deficiency: Zinc matters, but only if you're actually low. In a small study, young men put on a zinc-restricted diet saw their testosterone fall sharply, and older men with marginal zinc deficiency saw it rise after several months of supplementation. [12] In a trial of men already getting enough zinc, a high-dose zinc supplement made no difference. [13]
• Vitamin D deficiency: This is a weaker case. Low levels are linked with lower testosterone, and a small trial in overweight, vitamin D–deficient men found testosterone rose over a year of supplementation. [14] But a larger trial in men who had low testosterone and only mild vitamin D insufficiency found no meaningful rise. [15] A true deficiency of either nutrient is worth correcting, just not as a testosterone plan on its own.
• Medications: Some suppress the brain's signal directly. Long-term opioid use is the classic example, and so are glucocorticoids like prednisone taken for long stretches. Past anabolic steroid use belongs here too, since the brain can take months or longer to restart a signal it hasn't needed. [1,2]

What About Testosterone Boosters?

The claims on a testosterone booster bottle usually run well ahead of the evidence. When researchers reviewed 50 popular boosters, 90% claimed to raise testosterone, yet of the ingredients inside them, only about a quarter had any published data showing an increase. About one in ten had data showing a decrease, and most had never been studied for their effect on testosterone at all. [16] We’ll cover boosters in more depth in Testosterone Boosters and Supplements (coming soon), but the short version is that a booster is no substitute for finding the cause.

What a Real Plan Looks Like

Finding the cause is where a good evaluation starts, not where it ends. A real plan does three things:

• Names the cause.
• Sets a goal.
• Sets a date to check whether it's working.

If it isn't working, the plan changes.

Sometimes fixing the cause is enough. Other times, treatment makes sense alongside it. That's especially true when the cause can't be fixed, or when your symptoms are wearing you down while you work on it. Treating Low Testosterone: Options and Expectations covers what therapy can change and what it can't promise.

If you want kids someday, say so before you start anything, because it changes which options make sense. [3]