Running on Empty: Low T, Fatigue, Mood, and Brain Fog

Quick recap: in Part 1 of The Low T Files, we met Mike, 47, whose sex drive and morning wake-up call had both gone missing. That was the first clue.

Now it’s 2:30 on a Tuesday afternoon, and Mike is staring at the same email he opened 20 minutes ago. He’s read the first line four times. His coffee is cold (third cup, if anyone’s counting). His coworker asks a simple question, and Mike snaps at him like he just insulted his fantasy football team.

Then he gets home, collapses on the couch, and wonders why he feels like a phone that won’t hold a charge, no matter how long it’s plugged in.

Tired. Cranky. Foggy. Is that low testosterone, or is that just being a grown man with a mortgage?

Honest answer: it could be either. Let’s dig in.

Can Low Testosterone Make You Tired?

Yes, low testosterone can cause fatigue, low energy, and low motivation. But fatigue is what doctors call a nonspecific symptom. Translation: it has a lot of possible causes, and low T is only one of them.

Here’s what the research says:

• A meta-analysis of more than 4,400 men found that men with low testosterone were more likely to report fatigue than men with normal levels (American Urological Association, Testosterone Deficiency Guideline, 2024).
• The link gets stronger the lower testosterone goes. In one study of men with diabetes, 68% of men with very low testosterone reported fatigue, compared with only about half of men with higher levels (American Urological Association, 2024).
• The American Urological Association specifically calls out afternoon fatigue as a possible low T pattern. Hello, Mike’s 2:30 slump.

The Endocrine Society lists decreased energy, motivation, initiative, and self-confidence among the signs associated with testosterone deficiency (Bhasin et al., Journal of Clinical Endocrinology and Metabolism, 2018).

What Low T Fatigue Can Feel Like

• You wake up tired even after a full night’s sleep
• You crash hard in the afternoon
• Workouts feel harder, and you skip more of them
• You’ve lost your “get up and go” for hobbies you used to love
• You feel less confident or less driven at work

Low Testosterone and Mood: Irritable, Flat, or Just “Blah”

Mike isn’t sad, exactly. He’s just… flat. Less patient. Less interested. The guy who used to plan weekend trips now just wants everyone to leave him alone.

Low testosterone is linked to low mood, irritability, and a higher risk of depression in men. Some of the strongest evidence:

• Older men with low testosterone had about three times the risk of developing depression compared with men with normal levels in one study, and low T still predicted earlier onset of depression after adjusting for age and other health conditions (American Urological Association, 2024).
• A huge UK Biobank study of more than 133,000 men ages 40 to 70 found that low testosterone, especially low free testosterone, was tied to a higher risk of depression. The link was strongest in middle-aged men (He et al., Journal of Affective Disorders, 2026). Fun twist: abnormally high testosterone was also linked to higher depression risk. More isn’t automatically better.
• The Endocrine Society notes an association between low T and a long-lasting, low-grade type of depression that often shows up later in life (Bhasin et al., 2018).

Why Low T and Depression Are So Easy to Mix Up

Low T and depression share a lot of the same symptoms: low mood, loss of interest in things you used to enjoy, fatigue, and trouble thinking clearly (Hauger et al., Reviews in Endocrine and Metabolic Disorders, 2022). The reverse is true, too. Stress, chronic fatigue, and depression can cause many of the same symptoms men blame on low T (American Urological Association, 2024).

That’s exactly why guessing doesn’t work. The right move is to check both your mood and your hormones.

Low Testosterone and Brain Fog: Where Did My Focus Go?

Walking into a room and forgetting why. Losing your train of thought mid-sentence. Rereading the same paragraph (we see you, Mike).

Poor concentration and memory are recognized symptoms associated with low testosterone (Bhasin et al., 2018). Doctors sometimes describe it as “clouded cognition.”

A study of U.S. adults age 60 and older found that men with testosterone under 300 ng/dL had higher odds of scoring poorly on memory and thinking tests. And here’s the kicker: men who had both low testosterone and less than 7 hours of sleep had the highest odds of all (Liu et al., Psychiatry Research, 2025).

So if you’re running on low T and low sleep, your brain is basically trying to run a marathon in flip-flops.

The Sleep Connection

Low T and sleep have a complicated relationship. Sleep disturbance and increased sleepiness are both on the Endocrine Society’s list of symptoms associated with testosterone deficiency (Bhasin et al., 2018).

And poor sleep can make everything else on this list worse: fatigue, mood, focus, even libido. If you snore loudly, wake up gasping, or your partner has threatened to sleep on the couch because of the noise, mention it to your provider. Sleep apnea is a common cause of fatigue that’s worth ruling out.

Plot Twist: It Might Not Be Low T

Here’s where we keep it real, because your time (and your health) matter.

A 2026 JAMA review notes that fatigue, brain fog, or low mood on their own usually aren’t enough reason to test for low T (Anawalt et al., JAMA, 2026). These symptoms become much more meaningful when they show up alongside the more specific signs from Part 1: lower libido and fewer morning erections.

Other common causes of fatigue, low mood, and brain fog in men include:

• Poor sleep or sleep apnea
• Depression or anxiety
• Chronic stress and burnout
• Thyroid problems
• Anemia
• Diabetes or blood sugar problems
• Too much alcohol
• Medications, including opioids and steroids (which can also lower testosterone)
• Excess weight, which is also the most common reversible cause of low T (Anawalt et al., JAMA, 2026)

The good news? A good men’s health workup can look at all of these at once.

Will Fixing Low T Fix My Energy and Mood?

Straight talk: the research is mixed.

• Testosterone therapy is great at improving sexual function in men with confirmed low T, but its effects on energy, mood, and depressive symptoms tend to be small (Grossmann et al., Journal of Clinical Endocrinology and Metabolism, 2023).
• Some major trials showed improvements in mood and energy, while others didn’t. Men with truly low testosterone seemed more likely to benefit than men with borderline levels (Thompson et al., Nature Reviews Urology, 2026).
• Studies so far haven’t shown that testosterone therapy improves memory or thinking (American Urological Association, 2024).

That’s why the goal isn’t just “get on testosterone.” The goal is to find out what’s actually draining your tank and fix that. At Maze Men’s Health, that’s exactly how we approach it.

Your Low T Energy and Mood Checklist

Ask yourself honestly:

• Am I tired most days, even with decent sleep?
• Do I crash in the afternoon?
• Am I more irritable or short-tempered than usual?
• Have I lost interest in hobbies, workouts, or social plans?
• Is my focus or memory slipping?
• Have I also noticed a lower sex drive or fewer morning erections?

If you checked that last box along with a few others, it’s time to stop guessing and get tested.

Coming Up Next in The Low T Files

Mike’s getting closer to answers. Here’s what’s next:

• Part 1: Is It Low T or Just Life? The First Signs of Low Testosterone
• Part 2: Running on Empty: Low T, Fatigue, Mood, and Brain Fog (you are here)
• Part 3: Bedroom Blues and Body Changes: Low T vs. Erectile Dysfunction, Muscle Loss, and Belly Fat
• Part 4: The Silent Signs: Bone Loss, Anemia, Hot Flashes, and Fertility
• Part 5: Mike Gets Tested: What Happens at a Low T Appointment (and What Comes Next)

Tired of Being Tired? Let’s Find Out Why.

You don’t have to white-knuckle your way through another afternoon crash. Whether it’s low T, poor sleep, stress, or something else, the first step is the same: real answers from a real men’s health team.

Book your evaluation at Maze Men’s Health today. We’ll talk through your symptoms, order the right morning labs, and look at the whole picture, not just one number.

Schedule Your Appointment Now

Your energy, your mood, and your focus are worth fighting for. Let’s get you back to full battery.

Sources

1. American Urological Association. “Testosterone Deficiency Guideline.” American Urological Association, 2024.
2. Bhasin S, Brito JP, Cunningham GR, et al. “Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline.” Journal of Clinical Endocrinology and Metabolism, 2018.
3. Anawalt BD, O’Connor KM, Grossmann M. “Adult Male Hypogonadism: A Review.” JAMA, 2026.
4. He D, Gou Y, Wei W, et al. “The Complex Relationship Between Testosterone Imbalance and the Risk of Depression and Anxiety in Men.” Journal of Affective Disorders, 2026.
5. Liu H, Chen X, Ma G, et al. “The Interactive Effects of Low Testosterone and Sleep Insufficiency on Cognitive Impairment: Evidence From the NHANES 2011–2014.” Psychiatry Research, 2025.