Common Side Effects of Fosamax (Alendronate)
The most common side effects of alendronate are gastrointestinal in nature, particularly stomach pain, heartburn, nausea, constipation, diarrhea, and upset stomach, along with musculoskeletal pain affecting bones, joints, or muscles. 1
Gastrointestinal Side Effects
Upper GI Tract Effects (Most Common)
The FDA label identifies the following as the most frequently reported adverse effects:
In a large pharmacovigilance study of nearly 12,000 patients, dyspeptic conditions had the highest incidence density at 32.2 per 1000 patient-months, followed by nausea/vomiting at 20.8 per 1000 patient-months, and abdominal pain at 13.8 per 1000 patient-months 2. These gastrointestinal events were the most frequently reported reasons for discontinuing alendronate 2.
Esophageal Complications (Serious but Less Common)
Esophageal irritation represents a critical safety concern with oral alendronate administration. The American Society of Clinical Oncology guidelines specifically note that oral bisphosphonates like alendronate are associated with esophagitis, dysphagia, and gastric ulcers 3.
The FDA label warns that alendronate may cause local irritation of the upper gastrointestinal mucosa, with reported esophageal adverse experiences including 1:
- Esophagitis
- Esophageal ulcers
- Esophageal erosions (occasionally with bleeding)
- Esophageal stricture or perforation (rare but serious)
These esophageal complications can be severe enough to require hospitalization 1. A postmarketing analysis found that 199 patients reported esophageal adverse effects, with 51 (26%) categorized as serious or severe, and 32 (16%) requiring hospitalization 4.
Musculoskeletal Side Effects
Pain in bones, joints, or muscles is a common side effect listed in the FDA label 1. More concerning, the FDA warns that severe and occasionally incapacitating bone, joint, and/or muscle pain has been reported in post-marketing experience with bisphosphonates used for osteoporosis 1. This severe musculoskeletal pain warrants consideration for drug discontinuation 5.
Other Common Side Effects
The FDA label also notes that allergic reactions may occur, including hives or swelling of the face, lips, tongue, or throat 1. Additionally, worsening of asthma has been reported 1.
Critical Risk Factors for Esophageal Complications
The risk of severe esophageal adverse effects is significantly increased when patients 1, 4:
- Lie down after taking the medication (rather than remaining upright for at least 30 minutes)
- Fail to swallow the tablet with a full glass (6-8 ounces) of water
- Continue taking alendronate after developing symptoms of esophageal irritation
- Have preexisting esophageal disorders (such as Barrett's esophagus, dysphagia, or other esophageal diseases)
- Swallow the tablet with little or no water 4
Comparative Safety Profile
The ASCO guidelines indicate that while both oral and IV bisphosphonates are associated with adverse events, oral administration carries a higher risk of esophageal and gastric complications compared to intravenous formulations 3. This is an important consideration for patients who cannot tolerate oral bisphosphonates 5.
When to Stop Alendronate Immediately
Patients must discontinue alendronate and seek immediate medical attention if they develop 1:
- Chest pain
- New or worsening heartburn
- Trouble or pain when swallowing (dysphagia or odynophagia)
- Retrosternal pain
Clinical Pitfall to Avoid
The most critical error is failing to provide or ensure patient understanding of proper administration instructions 1. The FDA emphasizes that proper dosing instructions must be provided to and understood by the patient, as improper administration dramatically increases the risk of serious esophageal complications 1. In patients who cannot comply with dosing instructions due to mental disability, alendronate should only be used under appropriate supervision 1.