What You Need to Know About Alendronate Side Effects

Alendronate (brand name Fosamax) is one of the most widely prescribed medications for osteoporosis. It works by slowing bone loss and can significantly reduce your risk of fractures. But like all medications, it comes with potential side effects.

Most people tolerate Alendronate well — especially when they follow the dosing instructions carefully. Still, it's important to know what's normal, what's not, and when to call your doctor.

What Is Alendronate?

Alendronate is a bisphosphonate — a class of drugs that slows down the cells responsible for breaking down bone (osteoclasts). It's FDA-approved for treating and preventing osteoporosis in postmenopausal women, treating osteoporosis in men, managing glucocorticoid-induced osteoporosis, and treating Paget's disease of bone.

The most common dose is 70 mg taken once a week. For more details, see our full guide on what Alendronate is and how it works.

Common Side Effects

These are the side effects that show up most often in clinical studies and real-world use. They're usually mild and may improve as your body adjusts to the medication:

• Heartburn or acid reflux — The most frequently reported side effect. Following dosing instructions (staying upright, taking with water only) helps reduce this.
• Upset stomach or nausea — May happen especially in the first few weeks of treatment.
• Stomach pain or abdominal discomfort — Tends to be mild for most people.
• Diarrhea — Usually temporary and resolves on its own.
• Constipation — Less common than diarrhea but can occur.
• Bone, muscle, or joint pain — Some people notice aching in their bones or joints after starting Alendronate. This is usually mild.
• Headache — Occasionally reported, typically goes away with continued use.

Most of these gastrointestinal side effects are directly related to how Alendronate is taken. The drug can irritate the esophagus and stomach lining, which is why the dosing instructions are so specific: take it first thing in the morning, with a full glass of plain water, on an empty stomach, and stay upright for at least 30 minutes.

Serious Side Effects

These are less common but require immediate medical attention:

Esophageal Problems

Alendronate can cause esophageal ulcers, erosions, or narrowing (stricture). Symptoms to watch for include:

• Difficulty swallowing or pain when swallowing
• Chest pain
• New or worsening heartburn that doesn't go away

Call your doctor immediately if you experience any of these. Stop taking Alendronate until you speak with your provider.

Osteonecrosis of the Jaw (ONJ)

This rare condition involves deterioration of the jawbone. It's more common in cancer patients receiving high-dose IV bisphosphonates, but has been reported with oral Alendronate as well. Risk factors include:

• Dental surgery or tooth extraction
• Poor dental hygiene
• Use of corticosteroids
• Cancer or chemotherapy

Tell your dentist you're taking Alendronate before any dental procedures. Symptoms include jaw pain, swelling, numbness, or loose teeth.

Atypical Femoral Fractures

Long-term use of bisphosphonates (typically more than 3-5 years) has been associated with unusual fractures of the thigh bone (femur). These fractures can occur with minimal or no trauma. Warning signs include:

• Dull, aching pain in the thigh or groin area
• Pain that gets worse with activity

If you develop thigh or groin pain while taking Alendronate, tell your doctor right away.

Severe Musculoskeletal Pain

Some people develop severe bone, joint, or muscle pain that goes beyond the mild aching listed under common side effects. This can start days, months, or even years after starting treatment. If the pain is significant, your doctor may recommend stopping Alendronate.

Hypocalcemia (Low Blood Calcium)

Alendronate can lower blood calcium levels, especially if you're not getting enough calcium and vitamin D in your diet. Symptoms include muscle cramps, spasms, tingling in the fingers or around the mouth, and in severe cases, seizures. Your doctor should check your calcium levels before starting treatment.

Side Effects in Specific Populations

Older Adults

Alendronate is commonly used in older adults and generally doesn't require dose adjustments for age. However, older patients may be more sensitive to gastrointestinal side effects and should be especially careful about the upright-posture requirement to avoid falls.

People with Kidney Problems

Alendronate is not recommended if your kidney function is significantly impaired (creatinine clearance below 35 mL/min). If you have kidney issues, your doctor will need to choose a different medication.

People Taking NSAIDs

If you regularly take NSAIDs like Ibuprofen, Aspirin, or Naproxen, be aware that combining them with Alendronate increases the risk of stomach and esophageal irritation. Talk to your doctor about managing this risk. For a full list of interactions, see our guide on Alendronate drug interactions.

How to Manage Side Effects

Many Alendronate side effects can be minimized by following the correct dosing procedure:

• Take it first thing in the morning on an empty stomach
• Use a full glass (6-8 oz) of plain water only — not coffee, juice, or mineral water
• Stay fully upright (sitting or standing) for at least 30 minutes after taking it
• Don't eat, drink, or take other medications for at least 30 minutes
• Don't crush, chew, or suck on the tablet — swallow it whole

Other tips:

• Take calcium and vitamin D supplements as recommended by your doctor — but not at the same time as Alendronate (wait at least 30 minutes)
• Keep up with dental checkups and tell your dentist you're on a bisphosphonate
• Report new symptoms promptly — don't wait for your next scheduled visit if something feels wrong

If weekly dosing causes stomach problems, ask your doctor about switching to the effervescent tablet (Binosto), which dissolves in water and may be gentler on the esophagus.

Final Thoughts

Alendronate is a well-established medication with decades of use behind it. For most people, the benefits of stronger bones and fewer fractures far outweigh the side effects. The key is taking it correctly and staying in communication with your doctor.

If you're just starting Alendronate or considering it, don't let the side-effect list scare you off. Talk to your provider about your specific risk factors, follow the dosing instructions carefully, and know what symptoms to watch for.

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