Perimenopause fatigue: why you're so tired
Perimenopause fatigue is one of the most common complaints in midlife. It can feel like dragging through the day, needing naps you never needed before, or hitting a wall by mid-afternoon. Hormonal fluctuation can absolutely contribute, but it is rarely the whole story.
An underactive thyroid (hypothyroidism) can cause fatigue, weight gain, low mood, and what patients describe as "brain fog", forgetfulness, sleepiness, and trouble focusing. In a large patient survey, more than 95% of people with hypothyroidism and brain fog reported all four symptoms together (Ettleson et al., 2022). A 2022 review in Thyroid concluded that these symptoms sometimes linger even after thyroid blood tests return to normal (Samuels & Bernstein, 2022).
Sleep and perimenopause brain fog
Short or poor sleep can mimic a hormonal storm. A 2024 meta-analysis of 154 experimental studies (over 5,700 participants) found that sleep loss reliably reduced positive mood and increased anxiety (Palmer et al., Psychological Bulletin, 2024). Randomized trials show sleep restriction also nudges body weight upward by changing appetite and energy use (Capers et al., Obesity Reviews, 2015), and short sleep is consistently linked to abdominal weight gain in long-term studies (Kohanmoo et al., 2024).
Stress shifts the body's chemistry
Chronically elevated cortisol, the main stress hormone, is linked to mood instability, memory and attention problems, and changes in fat distribution. Both too-high and too-low cortisol can impair thinking (Frontiers in Endocrinology, 2023).
Small nutrient gaps, real symptoms
Iron: Even without anemia, low iron is linked to fatigue and low mood. A 2025 meta-analysis found iron supplementation improved fatigue, anxiety, and short-term memory in non-anemic adults (Hadi et al., 2025).
Vitamin B12: Deficiency causes fatigue, low mood, and cognitive symptoms; supplementation helps most clearly in people who are genuinely low (Markun et al., Nutrients, 2021).
What whole-picture care looks like
A thoughtful workup usually means a focused history, a look at sleep and stress habits, and a basic lab panel, thyroid (TSH, free T4), ferritin, B12, and a metabolic screen, before assuming hormones are the whole story.
Two people with identical symptoms can have completely different reasons behind them. Finding the right reason is what makes treatment work.
This kind of evaluation is central to my Perimenopause & Menopause service.
Written by Michelle Mullins, AGACNP-BC, FNP-BC
Last reviewed/updated: July 14, 2026