Why Am I Always Tired? The Hidden Causes and the Tests to Run

Being worn out after a hard week is normal. Being tired all the time, even after a full night in bed, is your body telling you something. Your energy is made inside your cells, in tiny power plants called mitochondria, and it runs on a daily rhythm set by sleep, light and cortisol, fueled by iron, B vitamins, vitamin D and steady blood sugar. When one of those links runs low, you can feel exhausted while a basic screening test still reads normal.5

I learned this firsthand. After a spinal infection, I went through rounds of antibiotics and was completely healed, yet afterward I felt drained and exhausted, wired but tired no matter what I did. Advanced bloodwork and functional medicine testing finally showed why: my vitamin B2 was low, and my mitochondria weren't working properly. The B complex I'd been taking had only about 2 milligrams of B2, so I started taking around 60 milligrams a day, and my energy went through the roof.6 For me it was B2, and that's probably not the answer for most people; far more people likely have a B12 deficiency or another gap. The point is that the missing piece showed up on a blood test.

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This guide covers the causes worth checking first, the tests that find them and the plan that brings your energy back. If your tiredness shows up mainly as a cloudy head, see our guide to brain fog; if it hits right after meals, see why you feel tired after eating.

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Why am I always tired?

Tiredness that won't lift is common. In a survey of 15,283 adults aged 18 to 45 in southern England, 18.3% reported substantial fatigue lasting six months or longer, women more often than men, and only 1.4% of them put it down to chronic fatigue syndrome.7 Fatigue is also among the top 10 reasons people visit a primary care office.8

In my view, nutrient deficiencies are probably the single biggest driver of worn-out cellular energy, followed by inflammation, poor sleep and chronic stress, with toxins such as heavy metals and mold, and infections such as Epstein-Barr virus, on the list too.6

Finding the cause can take more than one visit. In a Dutch study of 571 people who brought a new bout of fatigue to their primary care practice, 46.9% received a diagnosis that could be linked to their fatigue within a year, most of those diagnoses came after the first appointment, and a clear physical disease turned up in 8.2%.9 That's why I'd rather test a full panel than guess, as the bloodwork section below lays out.

The common causes of constant tiredness, and where to start

Is your sleep the problem, even with 8 hours in bed?

In my episode on why people wake up tired, I put it plainly: "You might spend 8 hours in bed, so you assume that sleep isn't the problem, but hours in bed aren't the same thing as restorative sleep."5 I recommend around 8 hours a night, and at minimum 7.15 Cutting that short adds up faster than it feels. In a lab study of 48 healthy adults aged 21 to 38, people randomly assigned to 4 or 6 hours in bed for 14 nights built up deficits on tests of attention, memory and thinking speed. At 6 hours or less, the deficits matched up to two nights of no sleep at all, and because their own sleepiness ratings barely rose, they were largely unaware of how impaired they'd become.16

Short sleep also pushes your stress hormones off their rhythm, as the cortisol section below shows step by step.

The fixes cost nothing: the same wake-up time every day, a cool bedroom in the low to mid 60s, morning sunlight, and screens off 2 hours before bed.5 Keep caffeine to the morning and skip it after lunch.6 For a full reset, see our guide to sleep hygiene, these natural sleep aids and The Deep Sleep Protocol.

Could it be sleep apnea?

In obstructive sleep apnea, the airway narrows or closes again and again during the night, so you can spend 8 hours in bed and wake up exhausted. It's far from rare: a 2019 analysis estimated that 936 million adults aged 30 to 69 worldwide have it, 425 million of them moderate to severe; several of its authors worked for a maker of sleep apnea machines.17 If you snore, wake gasping or feel sleepy while driving, my Deep Sleep Protocol says to get a sleep apnea test before anything else, because no supplement fixes blocked breathing.10 If snoring is your only sign, that's still reason enough to ask.

Can low iron make you tired if you're not anemic?

I've said it bluntly: "For decades, here was the rule: if you're not anemic, iron isn't your problem, don't take it. The rule is wrong."5 A basic anemia screen checks hemoglobin, the iron-carrying protein in your red blood cells. Ferritin reflects the iron you have in storage, and it can scrape bottom while hemoglobin still looks fine.512 Low ferritin causes fatigue, hair loss and restless legs, and it starves your mitochondria of the oxygen they need to make energy.12

The Swiss trial behind those numbers enrolled 144 women aged 18 to 55 whose main complaint was fatigue, none of them anemic, and gave them 80 mg of iron a day or an identical placebo for 4 weeks; neither the women nor the researchers knew who got what. Among the 136 who finished, fatigue scores fell 29% on iron and 13% on placebo. The benefit showed up only in women whose ferritin was 50 or lower, which described 85% of them, and the iron's maker sponsored the study.2

A second placebo-controlled trial pointed the same way. In 198 menstruating women with fatigue, a ferritin under 50 and no anemia, 80 mg of iron a day for 12 weeks cut fatigue scores 47.7%, against 28.8% on an identical-looking placebo; the iron's maker designed and funded it.18 Pooling the trials, a 2018 review of iron in adults who were iron deficient without anemia found it eased self-reported fatigue (4 trials, 714 people), while treadmill-style fitness tests didn't change.19

Test first, then treat. Ask for a ferritin test plus a full iron panel. The functional range in my bloodwork protocol is 50 to 100 ng/mL for women and 75 to 150 ng/mL for men, and too much iron damages cells too, so you never take it on a guess.12 When ferritin is low, I recommend iron plus vitamin C every other day.5 Absorption research backs the spacing: in a randomized study of 40 iron-depleted young women, where everyone knew which schedule they were on, 60 mg of iron taken on alternate days was absorbed better than the same doses on consecutive days (21.8% versus 16.3% of the iron), and hepcidin, a hormone that blocks iron absorption, ran higher with daily dosing.20 Our guide to iron supplements covers the forms and how to take them.

Build your blood with food. Eat beets, lean red meat and steamed leafy greens, and add beef liver and sardines, each paired with vitamin C foods for better absorption.512 Keep red meat fresh, unprocessed and grass-fed. The WHO's cancer agency classifies processed meat of every kind, processed beef included, as a Group 1 carcinogen, largely on colorectal cancer data, and rates red meat itself Group 2A, probably carcinogenic.21 As I've said on my show, the studies that link red meat to poor health mostly reflect grain-fed and processed meat, not the fresh, grass-fed red meat I recommend.22 More iron-rich foods are in our full list.

Low ferritin also has a reason behind it. Heavy periods and gut problems that block absorption top the list in my protocol, and a low ferritin with no clear cause deserves a doctor's look for hidden blood loss.12

Adrenal fatigue: is it your cortisol rhythm?

Your body needs cortisol.11 It rises 30 to 60 minutes after you wake, gets you moving and mobilizes fuel, then falls through the day so you can sleep. The shape of that curve matters far more than any single value, and as my bloodwork protocol notes, a single morning blood draw misses the most important information: the rhythm.12 A 4-point saliva cortisol test is a great way to look at your actual cortisol levels at four points during the day.11

The curve tracks with how tired you feel. A British study of 4,299 adults with an average age of 61 measured saliva cortisol six times across one day. Low waking cortisol and a flat daily slope went with fatigue, and among people who weren't tired at the start, those same patterns predicted new fatigue two to three years later: people in the lowest third for waking cortisol had 1.5 times the odds of new fatigue compared with those in the highest third. Earlier fatigue didn't predict later cortisol, which suggests the rhythm changes come first.24

I cover adrenal fatigue because the exhaustion people describe is real, and the cortisol rhythm underneath it can be measured and improved. The name itself is debated. Mainstream endocrinology doesn't use it as a diagnosis: a 2016 systematic review of 58 studies, which found conflicting results across the cortisol tests used, concluded there was no substantiation that it is an actual medical condition and noted that no endocrinology society recognizes it.25 Whatever name you use, the daily cortisol rhythm underneath can be measured. Chronic stress, short sleep, blood-sugar swings and overtraining can knock it out of shape, showing up as flat curves, flipped patterns or too much total output, and that's the problem to fix.12 I've described it like this: "When life is relentless, your body pumps out cortisol to keep you going. It works for a while." Run that system too long, though, and you end up wired but tired: "You're exhausted all day, then oddly buzzing when you finally try to sleep."5

Here's how a short night ripples through that rhythm, step by step:

I notice this in myself. If I overwork, I'll wake up at 3 a.m. and sleep lightly afterward, because my cortisol runs too high. Glycine, phosphatidylserine and magnesium glycinate help me most, and the waking is also my signal that I need to work less and build in more down-time.5 Our guide to cortisol levels covers the rest of the rhythm.

Suspected low cortisol is tested, never self-treated. Truly low cortisol is treated as adrenal insufficiency, a separate and serious condition, until testing shows otherwise. The Endocrine Society recommends testing anyone with suggestive symptoms, using a short corticotropin (ACTH) stimulation test, or, when that test isn't possible right away, morning blood levels of ACTH and cortisol.27 Its warning signs are listed in When to get care below.

Why do I crash in the afternoon?

That 3 p.m. crash, with heavy eyes and the urge to nap, often traces back to blood sugar on a roller coaster.5 A sweet snack tends to make it worse. A 2019 analysis of 31 studies with 1,259 participants found that carbohydrate, mostly sugary drinks, didn't improve mood at any point afterward, and compared with a placebo it left people more tired and less alert within the first hour; it relieved fatigue only after hard exercise.28

I saw this in my own life. I used to do a lot of triathlons, and after I stopped, I kept eating the same, which was quite a few carbs, and I started getting tired in the afternoon. When I moved to more moderate carbs, more protein and more fiber, my energy held steady all day, and 2 or 3 p.m. felt no different from 10 a.m.5

On my show I put the fix in one line: "Eat your protein and fiber before the carbs, cut the added sugar and the refined flour, and take a 10-minute walk after meals."5 Small studies back the food order and the walk. In a pilot study where 11 adults with type 2 diabetes each ate the same meal in both orders, eating the vegetables and protein first and the carbohydrate last lowered blood sugar 36.7% at the one-hour mark.29 And when 10 inactive adults over 60 with borderline-high fasting blood sugar each tried three walking plans, three 15-minute walks after meals lowered 24-hour blood sugar about as much as one 45-minute morning walk (10% versus 8%), and they were the only plan that clearly lowered blood sugar in the 3 hours after dinner.30 See what normal blood sugar looks like, the insulin resistance diet, and the free Insulin Resistance & Prediabetes protocol.

Could your thyroid be the cause?

A slow thyroid is a classic driver of constant tiredness, and the standard screen often stops short of finding it. Your doctor should test more than TSH, thyroid-stimulating hormone: ask for free T3, free T4 and thyroid antibodies such as TPO too.5 My bloodwork protocol puts it this way: "TSH alone can miss thyroid dysfunction."12

Each piece of the full panel tells you something different. TSH is the signal from your pituitary gland, free T3 is the active hormone, free T4 is the storage form, and the antibodies show whether your immune system is attacking the gland. Hashimoto's autoimmunity heads the list of root causes in my protocol, followed by low selenium, zinc and iron and by chronic stress and high cortisol, which is why the iron and cortisol sections above matter here too.12 Our guide to thyroid problems and the free Hypothyroidism and Hashimoto's protocols go deeper.

Could low vitamin D, B12 or magnesium be draining your energy?

Low vitamin D, low B12 and low magnesium each drain energy, and each one shows up on a blood test.

Low vitamin D

Vitamin D works like a hormone, with receptors on nearly every cell in your body, and a low level is easy to find and fix.12 In a Swiss trial, 120 otherwise healthy adults with fatigue and a vitamin D level below 20 µg/L (20 ng/mL) took a single 100,000 IU dose of vitamin D3 or an identical placebo; neither they nor the researchers knew who got what. Four weeks later, 72% of the vitamin D group reported less fatigue, against 50% on placebo, and fatigue scores improved only in the vitamin D group; a second fatigue questionnaire pointed the same way, by a smaller margin that could have been chance (48% versus 37%).3

The vitamin D test is called 25-hydroxy vitamin D, and our guide to the benefits of vitamin D covers what else it does. How much to take is in the supplements section below.

Low B12

Vitamin B12 helps your cells make energy, and a standard B12 test can read normal while your cells are short. On my show I call MMA cellular B12 and a much better test than B12 alone.5 MMA (methylmalonic acid) builds up in your tissues when B12 is running low at the level of the cells, which makes it far more sensitive than serum B12.12

Two common medicines lower B12 over time. In the Diabetes Prevention Program, a trial that randomly assigned adults at high risk of diabetes to metformin or placebo, low B12 turned up more often on metformin when about 1,700 of them were tested at 5 years (4.3% versus 2.3%), and each year of metformin raised the odds of deficiency by 13%.31 In a California health-system study comparing 25,956 people with B12 deficiency with 184,199 without it, a 2-year or longer supply of acid-blocking proton pump inhibitors went with 65% higher odds of deficiency.32

If you take a B complex, start with a regular one and then try a methylated one; if the methylated form leaves you wired but tired, your body can't handle it, so go back to the regular version.5 See the benefits of vitamin B12 and the best B12 foods.

Low magnesium

The ATP your cells spend for energy is bound to magnesium when it's used, which is why magnesium matters so much for energy.512 Ask for red blood cell (RBC) magnesium, which measures what's inside your cells, rather than the usual blood level.5 Food comes first: see these foods high in magnesium and the signs of magnesium deficiency. To supplement, take 300 to 400 mg of magnesium glycinate in the evening, about an hour before bed, which helps sleep as well.10

How do stress and mood drain your energy?

Emotional strain drains energy as surely as a short night. In the English survey above, fatigue and psychological distress went together, and psychosocial reasons, such as work, family and lifestyle, were the explanation people gave most often for their tiredness.7 If low mood, loss of interest or hopelessness travel with your tiredness, treat them as part of the same picture and bring them up when you're tested; our guides to the signs of depression and natural remedies for depression can help. If thoughts of self-harm appear, go straight to When to get care.

I want to have a big impact with my life, so I always have to keep coming back to this: I'm not just a piece of machinery created for productivity. I'm a child of God, and God wants me connecting with other people, having hobbies and enjoying my life.5 The single greatest thing that gives me energy every day is knowing that God has called me to love others.5

Build that into your days. Add 15 minutes of prayer and Bible reading in the morning, schedule a 15-minute walk around lunch, and stop working completely after dinner. Then take one day a week, Saturday or Sunday, and make it a Sabbath rest.5 Scripture puts the invitation plainly: "Come unto me, all ye that labour and are heavy laden, and I will give you rest" (Matthew 11:28, KJV).

How does movement affect your energy?

When you're exhausted, resting feels right, but long stretches of sitting lower your energy further.5 A 2006 analysis of exercise trials found that regular exercise raised feelings of energy and lowered fatigue compared with control groups, a small-to-moderate boost on average; the trials that used a placebo comparison and tested exercise alone found no effect.33 In a University of Georgia trial, 36 sedentary young adults with persistent fatigue were randomly assigned to low- or moderate-intensity cycling three times a week, or no exercise, for 6 weeks; both exercise groups felt more energetic, and the low-intensity group saw the bigger drop in fatigue.34

When your energy dips, a lot of times you need another 10-minute walk, not another coffee, because motion makes energy.5 The weekly goal is to walk a lot, strength train 2 to 3 days a week, and if you do hard cardio, make it one max-effort day of something like interval training, and no more.35 Punishing daily workouts and marathons drain your energy, and so does not moving.5

When exercise makes you worse

If exertion leaves you far worse afterward, a crash called post-exertional malaise, take it seriously. It's the most important symptom of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), exercise can trigger it, and the approach is pacing your activity within the energy you have.8

This one is personal. After my mom went through chemotherapy and beat cancer, she was diagnosed with chronic fatigue syndrome.52 If you'd asked her how she felt, she'd have used two words: exhausted and overwhelmed. She taught part-time, and when she got home she'd need to nap for an hour or two.3637 In Heal Your Cells, Dr. Will Cole and I describe chronic fatigue syndrome as burnout at the level of the mitochondria, and our free Heal Your Cells protocol is built around restoring that cellular energy.37

Could you be dehydrated?

Even mild dehydration can sap your energy. In a lab study of 25 young women, losing about 1.36% of body weight in fluid through exercise, with a water pill added in some sessions, lowered vigor and raised fatigue scores, made tasks feel harder and brought on headaches, though most thinking tests didn't change.38

My rule of thumb is half your body weight in ounces of water daily. Don't wait until you're thirsty: drink water first thing in the morning and front-load it earlier in the day, so it doesn't wake you at night.5 If you have a prescribed fluid limit for kidney or heart failure, follow that instead. Learn how much water to drink, the benefits of drinking water and the most hydrating foods.

Can medications or other conditions cause fatigue?

Yes. Some everyday prescriptions add to tiredness, and several medical conditions show up first as fatigue. Beta-blockers, used for blood pressure and heart conditions, added a small amount of reported fatigue in 15 placebo-controlled trials of more than 35,000 people: about 18 extra reports per 1,000 people a year, or one for every 57 treated.39 Metformin and acid blockers can lower B12 over time, as the B12 section above shows. If you suspect a prescription, don't stop it; the medication guidance in When to get care explains what to do.

A doctor also rules out conditions that can show up as fatigue first, including anemia, diabetes, heart, kidney and liver disease, infections, long COVID and ME/CFS.8 Sometimes I recommend testing for hidden infections, mold and heavy metals too, because a hidden infection or toxin can keep you tired.6

What blood tests should you get if you're always tired?

The ranges below are the functional (optimal) ranges from my 25 Root-Cause Bloodwork Markers protocol, with vitamin D from my episode on waking up tired. Conventional lab ranges are built to catch disease; functional ranges are narrower, so they flag a pattern earlier, when you can still feel tired while sitting inside the standard range.125 Testing shows you where your energy is leaking, and the results get read alongside your symptoms.

The labs to run when you're always tired

How we chose these labs: each one checks a common, correctable cause of tiredness covered on this page, and each result changes what you do next.

What supplements help when you're always tired?

These five are ranked by the strength of the human research behind them for tiredness.

What does traditional Chinese medicine say about fatigue?

Traditional Chinese medicine reads exhaustion as a pattern, and two of its patterns describe it directly: qi deficiency, a shortage of vital energy, and blood deficiency. In blood deficiency, as I've explained it, the blood isn't nourished enough and doesn't carry enough iron, oxygen and nutrients to get energy out to the rest of your body. The signs are exhaustion, sometimes dizziness when you stand up, pale lips and nails, poor sleep, thinning hair and, the one the tradition watches most closely, a pale tongue.5

The traditional answer is to build the blood: warming foods such as soups, beets, lean red meat and steamed leafy greens, with the herb dong quai.5 Those are the same iron-rich foods the iron section recommends, and the tradition's signs line up with what a ferritin test measures, so use the pale tongue as the tradition's sign and confirm it with ferritin.12 The tradition also uses acupuncture, and a 2023 clinical review lists it, along with exercise and cognitive behavior therapy, among the approaches that may ease some of the fatigue tied to chronic conditions.8

When to get care

Medications. If you think a prescription is adding to your tiredness, don't stop it or change the dose on your own; ask the doctor who prescribed it. That includes beta-blockers, metformin, acid blockers and antidepressants, which shouldn't be stopped abruptly, and thyroid medication, which you keep taking exactly as prescribed. If you take warfarin, check with the doctor who prescribes it before you add vitamin K2, CoQ10 or dong quai, since each can interact with it.474849

Supplement cautions:

• Iron. Take it only after a ferritin test and a full iron panel, since too much iron damages cells, and skip it if you have hemochromatosis or a high ferritin.12 Keep iron supplements away from children.

• Vitamin D. Dose to your blood level and retest; don't take high doses without testing.

• Magnesium. If you have kidney disease, check with the doctor who manages it before you take a supplement.

• Ashwagandha. In five documented cases of liver injury, people developed jaundice 2 to 12 weeks after starting it, and the four who were followed recovered within 1 to 5 months.50 Stop it and get checked if your skin or eyes turn yellow, your urine darkens or you itch all over. Skip it during pregnancy or while breastfeeding. If you have an overactive thyroid, or take thyroid medication or another drug it can interact with (immune-suppressing, seizure, sedative, blood-sugar or blood-pressure drugs), check with your doctor first.51

• Dong quai. Skip it during pregnancy or while breastfeeding.49

• Rhodiola. It can be activating, so take it in the morning rather than late in the day.35

The bottom line

Always tired: frequently asked questions

References

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15. Axe J. Why SLEEP is Medicine: My 4 Tips to Improve Energy. The Dr. Josh Axe Show, Episode 339. March 23, 2026.
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35. Axe J. 7 Science-Backed Ways to Lower Your Cortisol Fast. The Dr. Josh Axe Show, Episode 391. September 21, 2026.
36. Axe J. Top 10 Ways to Boost Mitochondrial Health for All-Day Energy. The Dr. Josh Axe Show. March 31, 2025.
37. Axe J, Cole W. Heal Your Cells. 2026. Chapter "Why We're Tapped Out" and the functional-range and supplement tables (book).
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50. Björnsson HK, Björnsson ES, Avula B, Khan IA, Jonasson JG, Ghabril M, et al. Ashwagandha-induced liver injury: A case series from Iceland and the US Drug-Induced Liver Injury Network. Liver Int. 2020;40(4):825-829. doi:10.1111/liv.14393. PMID:31991029
51. National Center for Complementary and Integrative Health. Ashwagandha: Usefulness and Safety. National Institutes of Health; last updated March 2023.
52. Axe J, Rubin J. The Biblio Diet. Hachette Book Group; 2025. ISBN 9781546008439. Chapter 2, "Nourish to Flourish": his mom's cancer and the chronic fatigue syndrome diagnosis that followed (written); Chapter 12, "A Biblical Spice Rack": ashwagandha "particularly effective for enhancing adrenal gland health, including alleviating adrenal fatigue" (written).

Dr. Josh Axe, DC, DNM, CNS

Doctor of Natural Medicine · Founder, DrAxe.com

Dr. Axe is a certified doctor of natural medicine, clinical nutritionist, and multiple New York Times bestselling author. He has spent 20+ years in clinical practice helping people heal at the root cause and founded one of the most-visited natural-health platforms in the world.

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