Korlym is a prescription medication used to control high blood sugar caused by Cushing’s syndrome. Specifically, it’s approved for adults with endogenous Cushing’s syndrome who also have type 2 diabetes or glucose intolerance, and who either had surgery that didn’t fully resolve the condition or can’t have surgery at all. It’s the brand name for mifepristone, taken as a daily oral tablet.
How Cushing’s Syndrome Causes High Blood Sugar
Cushing’s syndrome happens when your body produces too much cortisol over a long period. Cortisol is a stress hormone that, among many things, raises blood sugar levels. In healthy amounts, this is useful. But when cortisol stays chronically elevated, it can push blood sugar high enough to cause type 2 diabetes or glucose intolerance. That’s the specific problem Korlym targets.
The most common cause of endogenous Cushing’s syndrome is a small tumor on the pituitary gland that signals the adrenal glands to overproduce cortisol. Surgery to remove this tumor is the first-line treatment. But surgery doesn’t always work completely, and some patients aren’t candidates for it due to tumor location or other health factors. That’s where Korlym fits in: it’s a second-line option for managing the metabolic consequences when surgery isn’t enough.
How Korlym Works
Korlym takes an unusual approach. Rather than reducing the amount of cortisol your body makes, it blocks cortisol from attaching to its receptors in your tissues. Think of it like changing the locks so cortisol can’t get through the door. At the doses used for Cushing’s syndrome, mifepristone specifically blocks a receptor called GR-II, which is where cortisol binds to exert its effects on blood sugar and other metabolic processes.
This mechanism creates a counterintuitive situation: cortisol levels in your blood actually rise during treatment, sometimes significantly. Your body senses that cortisol isn’t working at the tissue level and compensates by making more. But because the receptors are blocked, those higher levels don’t translate into worsened symptoms. This also means that standard blood tests measuring cortisol can’t be used to gauge how well the medication is working or whether cortisol is being blocked too aggressively. Your doctor will instead track improvements in blood sugar control and clinical symptoms.
What Treatment Looks Like
Treatment starts at 300 mg taken once daily by mouth. The dose can be gradually increased based on how well your blood sugar responds and how you tolerate the medication. The maximum dose is 1,200 mg per day, though it should never exceed 20 mg per kilogram of body weight. Dose increases happen over time, not all at once, giving your body and your care team a chance to assess the response at each level.
Common Side Effects
Korlym’s side effects are well documented from clinical studies. In a trial of 50 patients with Cushing’s syndrome, the most frequently reported issues were:
- Nausea: 48% of patients
- Fatigue: 48%
- Headache: 44%
- Thickening of the uterine lining: 38% of women monitored by ultrasound
- Low potassium levels: 34%
These are high rates, meaning most patients will experience at least one of these. Nausea and fatigue are the most common, affecting roughly half of all people who take it. For women, the thickening of the uterine lining is significant enough that monitoring with ultrasound is part of the treatment plan.
The Potassium Problem
Low potassium is one of the more serious concerns with Korlym. In clinical studies, 44% of patients developed hypokalemia (potassium levels that dropped below the normal range). Potassium is critical for heart rhythm and muscle function, so this isn’t something to take lightly.
Your potassium levels need to be normal before starting Korlym. Once treatment begins, levels are typically checked one to two weeks after each dose increase and regularly throughout treatment. Low potassium can develop at any point, not just in the early weeks, which is why ongoing monitoring matters. If potassium drops, it’s treated with supplements. In stubborn cases, a second medication that blocks a different hormone pathway may be added to help potassium stay in range.
Pregnancy and Korlym
Korlym carries a boxed warning, the FDA’s most serious safety label, related to pregnancy. Mifepristone blocks progesterone receptors at lower doses, and progesterone is essential for maintaining a pregnancy. Taking Korlym during pregnancy can cause pregnancy loss. Pregnancy must be ruled out before starting treatment, and effective contraception is required for women of reproductive age throughout the course of therapy. Hormonal contraceptives may be less reliable because of how Korlym interacts with progesterone signaling, so non-hormonal methods are typically recommended.
Who Korlym Is Not For
Korlym is narrowly approved. It’s not a general treatment for Cushing’s syndrome or for high cortisol on its own. The FDA approval specifically requires the presence of type 2 diabetes or glucose intolerance alongside endogenous Cushing’s syndrome. It’s also not intended as a first option. Surgery remains the primary treatment for the tumors that cause most cases of Cushing’s, and Korlym is reserved for situations where surgery has already been tried or ruled out. Patients whose Cushing’s syndrome is caused by taking corticosteroid medications (exogenous Cushing’s) are not candidates for Korlym, since the treatment approach for that form of the condition is different.