You slept eight hours. You had your coffee. It's barely lunchtime—and you're already wondering how soon you can go back to bed.
Sound familiar?
Searches for “why am I always tired,” “vitamins for energy,” “why do I have no energy,” and “vitamin deficiencies that cause fatigue” reflect a problem many adults experience.
Fatigue can have dozens of possible causes, from poor sleep and stress to medical conditions. But two possibilities are easy to overlook: nutrient deficiencies and medication side effects.
Here's where to start looking.
First: What Does “Tired” Actually Mean?
Not all fatigue feels the same.
Maybe you're sleepy throughout the day. Maybe your muscles feel weak. Perhaps you're mentally foggy and have trouble concentrating. Or you simply don't have the energy you used to have.
Those differences matter because persistent fatigue isn't a diagnosis—it's a symptom.
If you're experiencing new, unexplained, severe, or persistent fatigue, especially with symptoms such as shortness of breath, chest pain, fainting, unusual bleeding, or significant unexplained weight changes, seek medical evaluation rather than trying to fix the problem with an energy supplement.
For everyday low energy, however, there are several areas worth investigating.
The “Low Energy” Nutrient Checklist
✓ Iron
Iron is essential for producing hemoglobin, which helps red blood cells carry oxygen throughout your body.
Iron deficiency anemia can cause tiredness, weakness, lack of energy, and problems with concentration and memory.
People with heavy menstrual periods, certain gastrointestinal conditions, and diets low in iron may have a greater risk of inadequate iron.
But here's the important part:
Don't automatically start taking iron because you're tired.
Too much iron can be harmful. A healthcare provider can determine whether testing is appropriate before you start supplementation.
Search connection: iron deficiency symptoms, low iron fatigue, vitamins for tiredness
✓ Vitamin B12
When people think about the best vitamins for energy, B12 is usually near the top of the list.
There's a legitimate reason for the association—but that doesn't mean taking extra B12 gives everyone an energy boost.
Vitamin B12 is necessary for healthy blood and nerve cells. A deficiency can cause fatigue, weakness, neurological changes, and a type of anemia called megaloblastic anemia.
Risk of deficiency may be higher among older adults, people following vegan or vegetarian diets, and people with certain gastrointestinal conditions.
Some medications can also affect B12 levels.
Which brings us to an important connection…
The Medication Factor: Could Your Prescription Be Contributing?
Sometimes fatigue isn't about what you're missing.
It may be related to something you're already taking.
Many prescription and over-the-counter medications list fatigue, tiredness, weakness, dizziness, or drowsiness among their possible side effects.
Here's a quick snapshot:
| Medication Type | Why You Might Notice Lower Energy |
|---|---|
| Some antihistamines | Can cause drowsiness or sedation |
| Certain blood pressure medications | May contribute to fatigue or dizziness |
| Some antidepressants | Drowsiness or fatigue can occur, depending on the medication |
| Certain anxiety medications | May have sedating effects |
| Muscle relaxants | Commonly cause drowsiness |
| Some pain medications | Can cause sedation or tiredness |
| Sleep medications | Effects can sometimes carry into the next day |
This doesn't mean you should stop taking your medication.
It means unexplained fatigue is worth mentioning to your pharmacist or prescriber, particularly if it started after beginning a new medication or changing your dose.
One Surprising Example: Metformin and Vitamin B12
Here's where medications and nutrient deficiencies can overlap.
Metformin, a widely used diabetes medication, can reduce vitamin B12 absorption and lower blood levels of B12. The NIH specifically lists metformin among medications that can interfere with vitamin B12 absorption.
That doesn't mean everyone taking metformin will become B12 deficient.
But if you're taking metformin and experiencing persistent fatigue, weakness, or other possible B12 deficiency symptoms, it's something worth discussing with your healthcare provider.
This is also a great example of why looking at your medications and supplements together can reveal things that are easy to miss when they're considered separately.
What About Vitamin D?
Vitamin D deficiency and fatigue is another popular search topic.
Vitamin D is essential for bone health, muscle function, and several other processes. People with very low vitamin D levels can experience muscle weakness and other symptoms.
But fatigue alone doesn't prove you have a vitamin D deficiency.
Your vitamin D status can be assessed with a blood test when clinically appropriate. If you're deficient, your healthcare provider can recommend an appropriate dose rather than guessing with an unnecessarily high-dose supplement.
And Magnesium?
Magnesium has become one of the biggest names in the supplement world, particularly for sleep, stress, muscle function, and relaxation.
Magnesium deficiency can cause symptoms including fatigue and weakness.
However, significant magnesium deficiency from diet alone is uncommon in otherwise healthy people.
If poor sleep is what's leaving you exhausted during the day, magnesium may come up in the conversation—but addressing the reason for poor sleep is just as important as choosing a supplement.
Before Buying an “Energy” Supplement, Try This 3-Step Test
STEP 1 — Look at your timeline.
When did the fatigue begin?
Think about recent medication changes, new supplements, changes in sleep, diet, stress, illness, or activity levels.
STEP 2 — Review what you're already taking.
Put every prescription, over-the-counter medication, vitamin, mineral, and supplement on one list.
Don't forget “occasional” products such as allergy medications or nighttime sleep aids.
STEP 3 — Ask whether testing makes more sense than guessing.
If a nutrient deficiency is suspected, a healthcare professional may recommend bloodwork rather than blindly adding supplements.
That's particularly important with nutrients such as iron, where taking more isn't necessarily harmless.
“What Vitamin Should I Take for Energy?”
This might be the wrong question.
If you aren't deficient in a particular nutrient, taking more of it doesn't necessarily translate into more energy.
The better questions are:
- Am I actually deficient in something?
- Could one of my medications be contributing to my fatigue?
- Am I sleeping well enough?
- Could something else be causing the change in my energy?
That's where personalized guidance beats grabbing the latest energy vitamin, B-complex, greens powder, or fatigue supplement off the shelf.
Bring the Question to Your Pharmacist
Your pharmacist sees something an Instagram supplement ad doesn't: the bigger picture.
At RM Island Pharmacy, we can review your prescription medications, over-the-counter products, vitamins, and supplements together. If your fatigue started after a medication change, you're wondering about a potential nutrient interaction, or you're considering adding a supplement for energy, talk with our pharmacist first.
Sometimes the answer may be a supplement.
Sometimes it may be medication timing, a possible side effect, or a conversation you should have with your doctor.
And sometimes the most valuable answer is simply:
“Before you spend money on that, let's figure out why you're tired.”
Persistent or unexplained fatigue can have many causes and should be evaluated by a healthcare professional. This article is for general educational purposes and is not intended to diagnose or treat any medical condition.
