Prednisone is a synthetic corticosteroid, meaning it’s a lab-made version of cortisol, the stress hormone your adrenal glands produce naturally. The active ingredient is prednisone itself, a compound with the molecular formula C₂₁H₂₆O₅. Beyond that single active ingredient, each tablet contains a handful of inactive fillers and binders that hold the pill together and help your body absorb it. Here’s what’s actually inside, how it works once you swallow it, and why your body handles it differently than you might expect.
The Active Ingredient
Prednisone tablets contain one active compound: prednisone. It belongs to a class of drugs called glucocorticoids, which mimic cortisol but are significantly more powerful. Prednisone is about four times more potent than hydrocortisone (the pharmaceutical name for cortisol). To put that in perspective, 5 mg of prednisone does roughly the same work as 20 mg of hydrocortisone.
Interestingly, prednisone itself isn’t what directly reduces inflammation. It’s actually a prodrug, which means your liver has to convert it into a different compound called prednisolone before it becomes fully active. This conversion happens quickly and is the body’s favored direction for the reaction. Some tissues, like your colon and kidneys, can convert prednisolone back into prednisone, but the net effect still favors activation. For most people with normal liver function, this conversion is seamless and doesn’t affect how well the drug works.
Inactive Ingredients in Prednisone Tablets
The rest of what’s in a prednisone tablet is filler and binding agents. These inactive ingredients vary slightly depending on the tablet strength, but they generally include the same core group:
- Anhydrous lactose: A form of milk sugar used as a filler to bulk up the tablet to a manageable size. If you have a lactose sensitivity, the amount here is very small, but it’s worth knowing it’s present.
- Microcrystalline cellulose: A plant-derived fiber that acts as a binder, holding the tablet together.
- Magnesium stearate: A lubricant that prevents the powder from sticking to manufacturing equipment.
- Sodium starch glycolate: A disintegrant that helps the tablet break apart in your stomach so the active ingredient can be absorbed.
- Colloidal silicon dioxide: An anti-caking agent found in the lower-strength tablets (5 mg and 10 mg).
- Talc: Another flow agent used in some tablet strengths.
Higher-strength tablets, like the 20 mg version, may also contain coloring agents. The 20 mg tablet typically includes yellow dyes (D&C Yellow No. 10 and FD&C Yellow No. 6) to distinguish it from other strengths. The 5 mg and 10 mg tablets are generally white and don’t contain added dyes. Generic manufacturers may use slightly different inactive ingredients, so if you have allergies to specific fillers, checking the package insert for your exact brand is worthwhile.
Available Tablet Strengths
Prednisone tablets come in five standard strengths: 1 mg, 2.5 mg, 5 mg, 10 mg, and 20 mg. Prednisone is also available as an oral solution (liquid) for people who have difficulty swallowing tablets. The wide range of tablet sizes reflects how differently the drug is dosed depending on the condition being treated. A short course for a severe allergic reaction might use higher doses for just a few days, while long-term use for something like lupus or rheumatoid arthritis often involves much lower daily amounts.
How It Works in Your Body
Once your liver converts prednisone into its active form, it enters your cells and changes how certain genes behave. Specifically, it tells your body to slow down production of the chemicals that drive inflammation. This is why prednisone can help with such a wide range of conditions: inflammation is a common thread in severe allergies, asthma flare-ups, arthritis, lupus, ulcerative colitis, multiple sclerosis relapses, and many skin and eye conditions. It also suppresses immune system activity more broadly, which is useful when the immune system is attacking the body’s own tissues but also explains why long-term use increases infection risk.
Prednisone is classified as intermediate-acting, with a biological half-life of 12 to 36 hours. That biological half-life is longer than the time the drug actually stays in your blood, because prednisone works by altering how your cells produce proteins. Those changes in protein production persist well after the drug itself has been cleared from your bloodstream. This is why a single morning dose can control symptoms throughout the day, and why the effects don’t vanish the moment you stop taking it.
Why It Differs From Cortisol
Your body makes cortisol every day, peaking in the early morning and dropping at night. Prednisone is structurally similar but has been modified to be stronger and longer-lasting. The four-to-one potency advantage over hydrocortisone means smaller doses achieve the same anti-inflammatory effect. For comparison, dexamethasone, a long-acting corticosteroid, is 25 times more potent than hydrocortisone, so only 0.75 mg is needed to match that same 20 mg hydrocortisone dose.
This potency difference matters because the side effects of corticosteroids, things like weight gain, blood sugar spikes, bone thinning, and mood changes, are tied to total exposure over time. Prednisone sits in a middle ground: strong enough to be effective at low tablet doses, but not so long-acting that it lingers in your system for days the way dexamethasone can. That intermediate profile is one reason prednisone remains one of the most commonly prescribed corticosteroids for conditions that need weeks or months of treatment.