Bisphosphonates are a class of drugs that slow bone loss by blocking the cells responsible for breaking down bone. They are the most widely prescribed medications for osteoporosis and have been shown to reduce the risk of spinal fractures by 60 to 70% within the first year of treatment. They’re also used for other conditions involving bone loss, including Paget’s disease and certain cancers that spread to bone.
How Bisphosphonates Work
Your bones are constantly being remodeled. Specialized cells called osteoclasts break down old bone, while other cells build new bone to replace it. In osteoporosis and similar conditions, the breakdown outpaces the rebuilding, and bones gradually become thinner and more fragile.
Bisphosphonates bind tightly to bone mineral and get absorbed by osteoclasts when those cells try to break bone down. Once inside the cell, the drug disrupts key processes the osteoclast needs to function. Some bisphosphonates block a critical enzyme, while older versions create toxic byproducts. Either way, the osteoclast slows down or dies, and bone breakdown drops significantly. Because the drug binds so firmly to bone, low levels continue to release over months or even years after you stop taking it.
Common Bisphosphonate Medications
Four bisphosphonates are FDA-approved for osteoporosis treatment:
- Alendronate (Fosamax), taken as a daily or weekly pill
- Risedronate (Actonel, Atelvia), available as a daily, weekly, or monthly pill
- Ibandronate (Boniva), taken as a monthly pill or quarterly injection
- Zoledronic acid (Reclast), given as an intravenous infusion once a year for osteoporosis, or every 3 to 4 weeks for bone cancers
All four reduce spinal fracture risk substantially. For hip fractures specifically, alendronate, risedronate, and zoledronic acid have demonstrated a 40 to 50% risk reduction. Ibandronate has not shown the same benefit for hip fractures. Non-spinal fracture risk drops by about 20 to 30% with the three more broadly effective options.
What Bisphosphonates Treat
Osteoporosis, particularly in postmenopausal women, is the most common reason these drugs are prescribed. They’re also used to prevent osteoporosis in people at high risk, such as those taking long-term corticosteroids. Beyond osteoporosis, bisphosphonates treat Paget’s disease (a condition where bone remodeling becomes chaotic and bones thicken abnormally) and help manage bone complications from cancers like breast cancer, prostate cancer, and multiple myeloma. Zoledronic acid is also used for hypercalcemia, a dangerous spike in blood calcium that can occur with certain cancers.
How to Take Oral Bisphosphonates
Oral bisphosphonates are notoriously finicky about absorption. Your body only absorbs a small fraction of the pill under ideal conditions, and food makes that fraction even smaller. Milk, coffee, orange juice, and any food can interfere with the drug getting into your system.
To get the most from each dose, take the pill first thing in the morning on a completely empty stomach. Swallow it with a full glass of plain water, nothing else. Then wait at least 30 minutes before eating, drinking anything other than water, or taking other medications. During that 30-minute window, stay upright. Don’t lie back down in bed. This isn’t just about absorption; staying upright protects your esophagus from irritation, which is one of the more common side effects.
If a yearly infusion sounds more manageable, zoledronic acid eliminates all of these daily or weekly routines. It’s given in a clinical setting over at least 15 minutes and covers you for a full year.
Side Effects
The most frequent complaint with oral bisphosphonates is upper digestive irritation. The drug can inflame the esophagus or cause small ulcers there, leading to heartburn, difficulty swallowing, or chest pain. This risk drops considerably when you follow the dosing instructions carefully, particularly the parts about staying upright and waiting before eating. People who skip these steps are much more likely to develop esophageal problems.
Flu-like symptoms (fever, muscle aches, fatigue) can occur after intravenous infusions, especially the first one. These usually resolve within a day or two.
Two rare but serious complications get the most attention. Osteonecrosis of the jaw is a condition where a section of jawbone loses its blood supply and begins to deteriorate. It occurs most often in cancer patients receiving high, frequent doses of intravenous bisphosphonates, and is uncommon at the lower doses used for osteoporosis. Dental procedures like tooth extractions can increase the risk, which is why your doctor may recommend completing any major dental work before starting treatment.
The second rare complication is atypical femur fractures. These are unusual breaks along the thighbone shaft that can occur with minimal trauma, sometimes preceded by weeks of dull thigh or groin pain. A large study of nearly 200,000 women published in the New England Journal of Medicine found that the risk of these fractures rises with longer use: after 8 or more years, the risk was substantially higher than in short-term users. Asian women faced roughly five times the risk compared to White women. Importantly, though, the absolute numbers remained very small. Among White women, 3 years of treatment prevented 149 hip fractures while causing only 2 atypical fractures. The tradeoff strongly favored treatment.
How Long Treatment Lasts
Bisphosphonates aren’t meant to be taken indefinitely. Because the drug accumulates in bone and continues releasing slowly after you stop, most people can take a “drug holiday” after several years. The FDA recommends periodic reassessment of whether continued treatment is still needed.
General guidelines suggest that people at low fracture risk may pause treatment after 3 to 5 years. Those at moderate risk typically continue for 5 to 10 years before considering a break. People at the highest risk, such as those with prior fractures, very low bone density, or ongoing corticosteroid use, may benefit from up to 10 years of treatment before pausing. During a holiday, your doctor might suggest an alternative medication to maintain bone protection.
The length of the holiday depends on your risk level too. Low-risk patients may stay off bisphosphonates indefinitely. Moderate-risk patients might resume after 3 to 5 years. High-risk patients could restart after just 1 to 2 years. Bone density measurements and blood markers of bone turnover help guide the decision to restart. If bone density drops or a fracture occurs during the holiday, treatment typically resumes.
For zoledronic acid specifically, a holiday may be considered after just 3 years of annual infusions, while oral options like alendronate and risedronate are generally continued for at least 5 years before pausing.
Who Should Not Take Bisphosphonates
People with significantly reduced kidney function are generally advised against bisphosphonates. The cutoff is an estimated filtration rate below 35 milliliters per minute, which corresponds to stage 4 chronic kidney disease. Below that threshold, the kidneys can’t clear the drug efficiently, and there’s a risk of further kidney damage. There also isn’t enough safety data in this group to know whether the benefits outweigh the risks.
People with active esophageal problems, such as strictures or difficulty swallowing, should avoid oral forms. Low blood calcium levels need to be corrected before starting treatment, since bisphosphonates can push calcium even lower by reducing bone breakdown. Vitamin D deficiency should also be addressed first, as adequate vitamin D is necessary for calcium absorption and healthy bone metabolism.