Alendronate is a prescription medication used to treat and prevent osteoporosis, the condition where bones become thin, weak, and prone to fractures. Sold under the brand name Fosamax, it belongs to a class of drugs called bisphosphonates. It’s one of the most widely prescribed bone-strengthening medications and is approved for several specific conditions and patient groups.
Conditions Alendronate Treats
Alendronate has four main uses:
- Postmenopausal osteoporosis: Both treatment of existing osteoporosis and prevention in women at risk. In postmenopausal women, it increases bone mass and reduces the incidence of fractures, including hip and spine fractures.
- Osteoporosis in men: Treatment to increase bone mass in men who have been diagnosed with osteoporosis.
- Glucocorticoid-induced osteoporosis: Treatment for men and women who are losing bone density because they take corticosteroid medications (such as prednisone) on a daily basis.
- Paget’s disease of bone: A condition where bone remodeling goes haywire, leaving bones soft, deformed, painful, or easily broken.
The most common reason people take alendronate is postmenopausal osteoporosis. After menopause, the drop in estrogen accelerates bone loss, and alendronate directly counteracts that process.
How It Works Inside Your Bones
Your body constantly breaks down old bone and replaces it with new bone tissue. Specialized cells called osteoclasts handle the breakdown side of this cycle. In osteoporosis, osteoclasts remove bone faster than it can be rebuilt, and you gradually lose bone density.
Alendronate works by disabling osteoclasts. It interferes with a chemical pathway these cells need to function, disrupting their internal structure and eventually triggering cell death. With fewer active osteoclasts chewing through bone, the balance tips back toward bone preservation. Over time, bone density increases because the bone-building cells can work without being outpaced.
How Effective It Is at Preventing Fractures
The clearest evidence comes from large clinical trials in postmenopausal women. In women with low bone density who hadn’t yet had a spine fracture, alendronate reduced the risk of vertebral fractures by 44%. That’s a meaningful reduction for a condition where a single spinal compression fracture often leads to more fractures down the line. The effect on hip fractures in this same group was smaller and not statistically significant, though hip fracture reduction has been demonstrated in higher-risk populations.
For people with Paget’s disease, alendronate normalizes the overactive bone turnover that causes pain and deformity. Treatment is typically recommended when blood markers of bone turnover are at least twice the normal level, or when a person is symptomatic or at risk for complications.
How You Take It
Alendronate comes as a daily or weekly tablet, with the weekly version being far more popular because it’s simpler. The way you take it matters a lot. The tablet needs to be swallowed first thing in the morning on an empty stomach with a full glass of plain water, not coffee, juice, or mineral water. After taking it, you need to stay upright (sitting or standing) and avoid eating or drinking anything else for at least 30 minutes.
These instructions aren’t optional. Alendronate is poorly absorbed to begin with, and food or other drinks reduce absorption even further. Staying upright protects your esophagus from irritation, which is one of the drug’s most common side effects.
Side Effects to Know About
The most common side effects involve the digestive system. Stomach pain is the most frequent complaint, followed by heartburn, difficulty swallowing, and irritation of the esophagus. These problems are more likely if you don’t follow the strict dosing instructions, particularly the requirement to stay upright and wait before eating.
Muscle pain can also occur and is sometimes a reason people stop taking the medication.
Two rare but serious complications are associated with long-term use. The first is osteonecrosis of the jaw, where a section of jawbone deteriorates. Symptoms include jaw pain, swelling, numbness, or loosening of teeth. The risk is higher if you’re having dental surgery while on the medication. The second is atypical femur fractures, unusual breaks in the thigh bone that can happen with minimal trauma. A dull, aching pain in the thighs, groin, or hips can be an early warning sign. Both complications are uncommon but become more likely the longer you take the drug.
How Long People Stay on It
Alendronate isn’t necessarily a lifelong medication. Because of the small but real risks that accumulate with prolonged use, clinical guidelines generally recommend reassessing after 3 to 5 years. For people whose fracture risk is low at that point, a “drug holiday,” a planned break from the medication, is often appropriate. Bisphosphonates bind tightly to bone and continue providing some protective effect even after you stop taking them, which makes a temporary pause feasible.
For people who remain at high fracture risk, continuing treatment or switching to a different medication is typically the better path. The decision depends on your bone density results, fracture history, and overall risk profile.
Who Should Not Take It
Alendronate is not appropriate for everyone with bone loss. People with certain esophageal problems, such as strictures or difficulty swallowing, shouldn’t take it because the tablet can cause severe esophageal irritation. It’s also not recommended for people who can’t stay upright for at least 30 minutes after taking it. Those with low calcium levels need to have that corrected before starting alendronate, since the drug alters how the body handles calcium. Kidney function also matters: people with significantly reduced kidney function generally cannot use it safely.