Prolia (denosumab) carries several serious risks, including a dangerous drop in blood calcium levels, rebound fractures if you stop taking it, and rare but severe jaw and thigh bone complications. The FDA added its most prominent warning, a boxed warning, to Prolia in 2024 specifically for patients with advanced kidney disease, after reports of hospitalizations, life-threatening events, and deaths linked to severely low calcium.
How Prolia Works in Your Bones
Prolia is a lab-made antibody injected under the skin once every six months. It works by blocking a protein called RANK ligand, which your body uses to build and activate the cells that break down old bone. By shutting down those bone-removing cells, Prolia slows bone loss and increases bone density over time.
This mechanism is effective, but it also explains most of Prolia’s dangers. Bone remodeling is a constant, tightly regulated cycle of breaking down and rebuilding. When you artificially suppress one side of that cycle, the consequences can ripple through calcium regulation, jaw healing, and long-term bone integrity.
Severely Low Calcium Levels
The most prominent FDA warning on Prolia concerns hypocalcemia, a dangerous drop in blood calcium. Because Prolia suppresses the cells that release calcium from bone into your bloodstream, calcium levels can fall sharply after each injection. For most people, this is manageable with calcium and vitamin D supplements. For people with advanced kidney disease, it can be life-threatening.
In a study of dialysis-dependent patients, 41.1 percent of those treated with Prolia developed severe hypocalcemia within 12 weeks, compared to just 2 percent of those taking an oral bisphosphonate. The highest risk window is two to five weeks after each injection, though dangerous drops can occur anywhere from two to ten weeks out. Of patients who developed severe hypocalcemia, 8.7 percent experienced seizures or cardiac arrhythmias within 30 days, and 3.3 percent died.
Severe hypocalcemia can show up as confusion, seizures, irregular heartbeat, fainting, facial twitching, uncontrolled muscle spasms, or tingling and numbness in the hands, feet, or around the mouth. It can also be completely silent, detected only through blood tests. The risk climbs with worsening kidney function and is highest in patients who also have a related condition called mineral and bone disorder.
Rebound Fractures After Stopping
One of the most unusual dangers of Prolia is what happens when you stop taking it. Unlike bisphosphonates, which bind to bone and linger for years after discontinuation, Prolia’s effects wear off within months. When they do, bone breakdown doesn’t just return to its previous rate. It overshoots, accelerating beyond where it was before treatment started. This rebound effect can cause rapid bone loss and a cluster of spinal fractures.
The UK’s Medicines and Healthcare products Regulatory Agency has warned that multiple vertebral fractures have been reported within 18 months of stopping or delaying Prolia, with some occurring in the first nine months. These aren’t single fractures. Patients have experienced several vertebrae collapsing in quick succession, sometimes without any fall or injury.
This means Prolia is essentially an open-ended commitment. Major medical organizations, including the Endocrine Society and the American Association of Clinical Endocrinology, recommend that patients never simply stop Prolia without transitioning to another bone-protecting medication. The standard approach is to switch to a bisphosphonate for one to two years after your last Prolia injection. If bisphosphonates aren’t appropriate, hormone therapy or similar medications may be used instead. Missing or delaying even a single dose can trigger the rebound effect, so staying on schedule is critical.
Osteonecrosis of the Jaw
Prolia can interfere with the jaw’s ability to heal after dental work, leading to a condition where a section of jawbone loses its blood supply and begins to die. This is called osteonecrosis of the jaw, and it causes pain, numbness in the mouth, difficulty swallowing, and trouble speaking. In severe cases, exposed bone becomes visible through the gums.
The risk is significantly higher in cancer patients receiving higher doses of bone-targeting drugs. In one study of breast cancer patients on antiresorptive therapy, 12 percent of those taking denosumab developed jaw osteonecrosis, compared to 3 percent on a bisphosphonate. For osteoporosis patients taking the standard Prolia dose (which is much lower than the cancer dose), the risk is considerably smaller but not zero.
To reduce this risk, you should not have invasive dental procedures within six weeks before or after a Prolia injection. If you need major dental work, coordinate timing with both your dentist and the provider prescribing Prolia. A dental screening before starting treatment is a sensible precaution, since untreated infections or planned extractions are best handled before the first dose.
Atypical Thigh Bone Fractures
Long-term use of Prolia is linked to atypical femoral fractures, an unusual type of break in the thigh bone. These fractures don’t happen from a major fall or impact. Instead, the bone develops stress damage over time, often starting as a dull ache in the thigh or groin weeks before the bone actually breaks. The fracture typically occurs along the shaft of the thigh bone rather than at the hip joint, which distinguishes it from a standard osteoporotic hip fracture.
The risk increases the longer you take Prolia. These fractures have been documented in patients on bone-modifying agents for several years, with one published case involving a patient who had been on oncologic doses for seven years. The paradox is real: a drug designed to prevent fractures can, over many years, make bone so uniformly dense that it loses its natural flexibility and becomes brittle in a different way. If you develop new or unusual thigh or groin pain while on Prolia, that symptom warrants prompt evaluation.
Infections and Immune Effects
RANK ligand, the protein Prolia blocks, plays a role in immune function beyond bone. Some patients on Prolia experience more frequent infections, particularly skin infections like cellulitis and urinary tract infections. Serious infections requiring hospitalization have been reported in clinical trials. While these events are uncommon, they’re worth being aware of, especially if you’re already prone to infections or have a weakened immune system.
Who Faces the Greatest Risks
Not everyone on Prolia faces the same level of danger. Your risk profile depends heavily on your kidney function, your dental health, and how long you’ve been on the drug. People with advanced chronic kidney disease (an estimated kidney filtration rate below 30) face the highest risk of severe hypocalcemia, particularly if they also have mineral and bone disorder. The FDA’s boxed warning applies specifically to this group, and the agency recommends weekly calcium monitoring for the first month after each injection in these patients.
People who have had or are planning dental surgery, tooth extractions, or implants face elevated risk of jaw complications. Those who have been on Prolia for five or more years should discuss atypical fracture risk with their provider. And anyone considering stopping Prolia for any reason, whether due to side effects, cost, or a change in treatment plan, needs a clear transition strategy in place before the next scheduled dose is skipped.