What does prednisone do to your body?
Last updated September 3, 2026.
Prednisone is a synthetic cortisol: it slams the brakes on inflammation and an overactive immune system - which is why it works so fast, and why the side effects scale with dose and duration. Short-course effects: insomnia, mood swings, bigger appetite and quick weight gain, fluid retention, raised blood sugar, stomach irritation. Longer courses add bone thinning, muscle weakness, easy bruising, and infection risk - and it can mask fever. Two rules: take it in the morning with food, and never stop a longer course suddenly - your body needs time to restart its own steroid production. Pymander is a free AI doctor, 24/7 by text, and can help you make sense of your course.
What to do
- Take it in the morning with food: matches your cortisol rhythm, spares your stomach.
- Expect the wired phase: insomnia and mood effects are the drug, not you.
- Guard against infection: it blunts defenses and can hide fever.
- Never stop suddenly after more than a couple of weeks: tapering is the rule.
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