The worst side effects of prednisone involve bone damage, psychiatric disturbances, blood sugar spikes, and suppression of your adrenal glands. Most of these serious effects are tied to higher doses and longer courses of treatment, but some can appear within days. Understanding which side effects are dose-dependent and which ones build over time helps you know what to watch for.
Psychiatric and Mood Changes
Prednisone’s effect on the brain catches many people off guard. Short-term, you may experience anxiety, insomnia, restlessness, irritability, or mood swings. At higher doses, the effects can escalate to mania, severe depression, aggression, or full psychosis. About 6% of patients exposed to steroids develop what researchers classify as severe psychiatric syndromes.
The risk climbs sharply with dose. At 40 mg per day or less, roughly 1.3% of patients develop significant psychiatric symptoms. Between 41 and 79 mg per day, that jumps to 4.6%. Above 80 mg per day, the rate hits 18.4%. These effects are generally reversible once the medication is stopped or reduced, but they can be frightening when they appear, especially if you weren’t expecting them. Insomnia and restlessness are among the most common complaints even at moderate doses.
Bone Loss and Joint Damage
Long-term prednisone use thins bones, increasing your risk of osteoporosis and fractures. This is one of the most significant concerns for anyone on the drug for months or years. Children on extended courses may also experience slowed growth.
A more severe complication is avascular necrosis, where blood supply to a bone (most often the hip) gets cut off, causing the bone tissue to die. A meta-analysis found that cumulative doses greater than 2 grams of prednisone (the equivalent of taking 20 mg daily for about three months) significantly raise this risk. At that threshold, the incidence of avascular necrosis was about 6.7%. Each additional 10 mg per day was associated with a 3.6% increase in the osteonecrosis rate. This is a serious, potentially irreversible condition that can require joint replacement surgery.
To protect your bones during treatment, your doctor will likely recommend calcium and at least 800 international units of vitamin D daily. Weight-bearing exercise like walking or dancing helps stabilize bone mass. A bone density test is often ordered before or early in steroid therapy, and medications to strengthen bones may be added if your density is already low. Reducing alcohol and avoiding smoking also lower your fracture risk.
Blood Sugar Elevation
Prednisone reliably raises blood sugar, even in people without diabetes. It does this by making your cells more resistant to insulin and prompting your liver to release more glucose. For people who already have diabetes, this can make blood sugar significantly harder to control and may require medication adjustments.
For most people, glucose levels return to normal after stopping the drug. But prolonged courses at higher doses can sometimes tip someone into steroid-induced diabetes, a condition that may or may not resolve completely. If you’re on prednisone for more than a few weeks, blood sugar monitoring is standard practice.
Adrenal Suppression
Your adrenal glands naturally produce a hormone equivalent to about 5 to 7 mg of prednisone each day. When you take prednisone, your body recognizes the external supply and dials down its own production. After three to four weeks of use, your adrenal glands can become significantly suppressed, meaning they lose the ability to respond normally to stress, illness, or injury.
This is why you cannot stop prednisone abruptly after extended use. Doing so can trigger adrenal insufficiency: fatigue, weakness, dizziness, nausea, and in severe cases, a life-threatening drop in blood pressure. Tapering involves gradually reducing your dose until you reach a low physiologic level (around 4 to 6 mg daily), then continuing to taper from there while your adrenal glands wake back up. If withdrawal symptoms flare during a taper, the dose is typically bumped back up temporarily and the taper stretched out over a longer period.
Increased Infection Risk
Prednisone suppresses your immune system, which is the whole point for many conditions but also leaves you more vulnerable to bacterial, viral, and fungal infections. This risk becomes more apparent with prolonged courses. One study found no meaningful increase in infection risk when the total cumulative dose stayed below 700 mg or when the daily dose was under 10 mg. Above those levels, your body’s ability to fight off infections declines noticeably, and wounds heal more slowly as well.
Weight Gain and Body Changes
Prednisone redistributes fat in characteristic ways: a rounder face (sometimes called moon face), fat buildup at the base of the neck, and thickening around the trunk. These changes reflect how the drug alters fat metabolism and tend to appear with prolonged use at higher doses. In one study, 46% of patients taking an average of 31 mg daily over three months developed visible changes including excess hair growth, spontaneous bruising, or altered wound healing.
Weight gain is driven partly by increased appetite and partly by fluid retention from elevated blood pressure. Prednisone commonly raises blood pressure, though this effect is usually temporary and resolves when the dose comes down.
Eye Problems
Long-term use can lead to cataracts or glaucoma. Most reports link cataract development to doses of at least 10 mg daily sustained for a year or longer. Glaucoma risk comes from increased pressure inside the eye. If you’re on prednisone for an extended period, periodic eye exams can catch these changes early.
Stomach and Digestive Irritation
Many people on prednisone report stomach pain, heartburn, or symptoms resembling an ulcer. Interestingly, a large meta-analysis of 93 randomized trials found no direct link between prednisone alone and actual ulcer formation. The real danger comes from combining prednisone with anti-inflammatory painkillers like ibuprofen or aspirin, which significantly raises the risk of gastrointestinal bleeding.
If you need to stay on low-dose aspirin for heart protection, a stomach-protective medication may be added. Taking prednisone after a full meal or with an antacid can reduce irritation. Black, tarry stools or severe abdominal pain are warning signs of bleeding that need immediate attention.
Kidney Stones
Prednisone increases the amount of calcium and uric acid your kidneys excrete. These substances can crystallize and form kidney stones, particularly with longer courses. Staying well-hydrated helps reduce this risk, though it doesn’t eliminate it entirely.
How Timing and Dose Shape Your Risk
Nearly every serious side effect of prednisone is tied to how much you take and for how long. Short courses of a few days to two weeks, even at moderately high doses, carry far less risk than months of low-dose therapy for most complications. The exceptions are psychiatric effects and blood sugar changes, which can show up within the first few days regardless of planned treatment length.
Bone loss, adrenal suppression, cataracts, infection vulnerability, and body composition changes are overwhelmingly long-term concerns. This is why doctors aim for the lowest effective dose and the shortest possible course. When prednisone is genuinely needed, the benefits typically outweigh these risks, but knowing what to watch for puts you in a better position to flag problems early.