Why am I so tired on my GLP-1?

Fatigue shows up in trials at around 10%, but in practice it’s mostly a secondary effect — the drug suppresses intake so effectively that people accidentally run their bodies on fumes. Diagnostic ladder: 1. Count the calories (roughly). If appetite suppression has you under ≈1,000–1,200 kcal/day, fatigue is the expected output. The fix isn’t pushing through; it’s engineering intake upward with calorie-dense, easy formats — shakes, Greek yogurt, nut butters — and possibly a dose hold (eating playbook). 2. Check the protein. Chronic protein shortfall reads as weakness and brain fog. Floor: ≈1.2–1.6 g/kg of goal weight, liquid if needed (how). 3. Hydration and electrolytes. Lightheadedness on standing, headaches, and afternoon crashes are classic under-drinking. Water plus occasional electrolytes (broth, low-sugar electrolyte mixes) — especially in the first month, when rapid early water-weight loss flushes sodium. 4. Sleep, paradoxically. Some users report disrupted sleep early on; others were chronically under-slept before and notice it now that food isn’t masking it. 5. The lab tier. Fatigue persisting past a month despite fixed intake deserves bloodwork: iron/ferritin, B12, thyroid (TSH), and glucose. Eating dramatically less narrows micronutrient intake — it’s why many weight programs add B12 support by default and why a basic multivitamin is cheap insurance. 6. Diabetes-specific: if you’re on insulin or a sulfonylurea, fatigue episodes can be hypoglycemia — check sugars, and make sure those doses were reduced when the GLP-1 started. The reassuring base rate: most GLP-1 fatigue is a first-month phenomenon that resolves as eating stabilizes and the body adapts. Fatigue that’s worsening at month three is a clinician visit, not a forum thread.