Alendronate (brand name Fosamax) is one of the most commonly prescribed osteoporosis drugs, and while it effectively reduces fracture risk, long-term use carries several side effects worth understanding. Most are rare, but their likelihood shifts meaningfully depending on how many years you take the medication.
How Alendronate Works Over Time
Alendronate belongs to a class of drugs called bisphosphonates. It works by interfering with the cells responsible for breaking down bone (osteoclasts), essentially blocking a chemical pathway these cells need to function and survive. With fewer active bone-dissolving cells, your bones retain more density.
The drug binds directly into bone tissue and stays there for years, even after you stop taking it. This is why its effects persist long after discontinuation, but it also means that side effects tied to over-suppression of bone turnover tend to emerge with prolonged use rather than in the first year or two.
Esophageal and Stomach Irritation
The most common complaint with alendronate is irritation of the esophagus, the tube connecting your throat to your stomach. Inflammation, ulceration, and erosion of the esophageal lining are well-documented effects, which is why the drug comes with strict instructions to take it with a full glass of water and stay upright for at least 30 minutes afterward.
In rare cases, long-term use can lead to esophageal stricture, a narrowing of the esophagus caused by chronic inflammation. Since alendronate was approved in Canada in 1996, only four cases of stricture were reported to Health Canada, so this is genuinely uncommon. There have also been reports linking long-term alendronate use to esophageal cancer, though the evidence remains limited. If you develop persistent heartburn, difficulty swallowing, or pain behind the breastbone, these symptoms deserve prompt attention.
Atypical Femoral Fractures
This is the side effect that gets the most discussion in the medical community. Ironically, a drug designed to prevent fractures can, over many years, contribute to an unusual type of fracture in the thighbone. These “atypical femoral fractures” occur in the shaft of the femur rather than at the hip, often with little or no trauma. They happen because prolonged suppression of bone remodeling can make bone brittle in a different way: the normal process of repairing micro-damage gets shut down too completely.
The risk is very low in the first few years. For the first one to two years of therapy, the rate is roughly 1.78 per 100,000 people per year. But with eight to ten years of continuous use, that number climbs to about 113 per 100,000 per year. A case-control study found that more than five years of bisphosphonate use increased the risk of these fractures by about 2.7 times. Many people notice a dull ache in the thigh or groin weeks before a full fracture occurs, so persistent thigh pain during long-term treatment is a warning sign worth reporting.
Jaw Bone Damage (Osteonecrosis)
Medication-related osteonecrosis of the jaw is a condition where a section of jawbone loses its blood supply and begins to die, typically after a dental extraction or other invasive dental procedure. It sounds alarming, and it is serious when it happens, but at osteoporosis-level doses the prevalence is very low: between 0.07% and 0.10% of patients taking oral bisphosphonates.
The risk increases with duration of use and is considerably higher in cancer patients receiving much larger intravenous doses of bisphosphonates. If you’re on long-term alendronate, maintaining good dental hygiene and informing your dentist about your medication before any procedures is a practical way to reduce your risk.
Severe Musculoskeletal Pain
Some people develop significant bone, joint, or muscle pain that goes beyond what you’d expect from normal aging or arthritis. This type of pain is different from the flu-like symptoms that sometimes occur in the first few days of treatment. It can appear anywhere from the same day you start alendronate to years later, with a median onset of about 14 days. The key feature: it typically resolves only when the medication is stopped. If new, unexplained musculoskeletal pain develops while you’re on alendronate, it’s worth considering the drug as a possible cause.
Heart Rhythm Changes
There is a signal linking bisphosphonates to atrial fibrillation, an irregular heart rhythm. An analysis of adverse event reports in the Journal of the American College of Cardiology found that atrial fibrillation was reported at disproportionately higher rates across most bisphosphonates. For alendronate specifically, the reporting odds ratio was 1.4 compared to other drugs in the database, a modest but statistically significant signal. This doesn’t prove causation, but if you have existing heart rhythm issues, it’s relevant context for a conversation about your treatment plan.
Eye Inflammation
Rarely, bisphosphonates can trigger inflammatory eye conditions including uveitis (inflammation inside the eye), scleritis (inflammation of the white outer coat of the eye), and episcleritis. Symptoms include redness, eye pain, light sensitivity, and blurred vision. With oral alendronate, onset is typically several days after starting or resuming the medication. In cases of scleritis specifically, the drug needs to be discontinued regardless of whether anti-inflammatory eye treatment is used.
Kidney Function Considerations
Alendronate is not recommended for anyone whose kidneys filter below a certain threshold, specifically a creatinine clearance under 35 mL/min. If your kidney function falls between 35 and 60 mL/min, no dose adjustment is needed. But kidney function can decline over years, so what was safe when you started the medication may need reevaluation after a decade of use.
Drug Holidays and Duration of Use
Because many of the most concerning side effects are tied to duration, medical guidelines now recommend reassessing after three to five years. The American Society for Bone and Mineral Research recommends that women who are not at high fracture risk after three to five years of treatment consider a drug holiday of two to three years. Alendronate’s long residence in bone means its protective effects don’t vanish immediately when you stop.
For women at high risk, meaning older age, a hip bone density T-score at or below negative 2.5, a history of major fracture, or fractures that occurred while on treatment, continuing for up to 10 years of oral therapy may be appropriate with periodic reassessment. The decision hinges on weighing the ongoing fracture prevention benefit against the accumulating risk of atypical fractures and other complications. A hip T-score between negative 2 and negative 2.5 was identified as a threshold where continued therapy showed clear benefit in clinical trials.