Fosamax (Alendronate) 5‑70 mg Tablets: Prescription Bisphosphonate for Postmenopausal Osteoporosis, Glucocorticoid-Induced Osteoporosis, and Paget’s Disease of Bone

Information last reviewed: May 2026 — for educational purposes only.

Fosamax (alendronate sodium) is the most widely prescribed bisphosphonate and the benchmark first-line pharmacological treatment for postmenopausal osteoporosis and other conditions causing pathological bone loss. It works by being selectively taken up by bone, particularly at sites of active resorption, where it inhibits farnesyl diphosphate synthase — a key enzyme in the mevalonate (cholesterol synthesis) pathway within osteoclasts. Without functional mevalonate pathway activity, osteoclasts undergo apoptosis (programmed cell death), dramatically reducing bone resorption. The net result is a shift in bone remodelling balance toward formation: bone mineral density (BMD) increases at the lumbar spine and hip over 1–3 years of treatment, and the risk of vertebral and hip fractures is reduced by approximately 40–50% in clinical trials. Alendronate has over three decades of post-marketing experience with a well-characterised safety profile.

The most critically important feature of alendronate is its strict oral administration protocol. Alendronate is extremely poorly absorbed orally (bioavailability ~0.7% under ideal conditions) with virtually zero absorption if taken incorrectly. The drug is also highly irritating to the oesophageal mucosa if it remains in prolonged contact, and oesophageal ulceration or erosion can be severe. These factors drive the specific, non-negotiable administration requirements that every patient must understand before starting therapy.

What Is Alendronate?

Alendronate sodium is a nitrogen-containing bisphosphonate — one of the most potent inhibitors of bone resorption available orally. Its bisphosphonate backbone (two phosphonate groups attached to a central carbon) binds avidly to hydroxyapatite crystals in bone mineral, concentrating selectively at resorption pits where osteoclasts are actively dissolving bone. This selectivity for bone and the drug's exceptionally long half-life in bone (estimated 10+ years) means that alendronate continues to exert anti-resorptive effects even after treatment is stopped — the basis for the "drug holiday" strategy used with bisphosphonates after 5 years of treatment to reduce the risk of atypical femoral fractures from bisphosphonate over-suppression of bone turnover.

Prescription Status

Alendronate is prescription-only in the United States and is not available over the counter. Treatment decisions require physician evaluation including DEXA scan T-scores, FRAX fracture probability assessment, and consideration of secondary osteoporosis causes. Duration of treatment and decision about drug holidays (typically after 5 years) should be made jointly by the patient and prescribing clinician.

Strengths and Available Forms

• Alendronate 5 mg tablet — daily dosing; for prevention of postmenopausal osteoporosis (lower doses than treatment) and for men and glucocorticoid-induced osteoporosis prevention
• Alendronate 10 mg tablet — daily dosing; for treatment of postmenopausal osteoporosis and Paget's disease of bone (40 mg/day for Paget's — 4× 10 mg/day)
• Alendronate 35 mg tablet — once-weekly dosing; for prevention of postmenopausal osteoporosis; significantly improves adherence compared to daily dosing
• Alendronate 70 mg tablet — once-weekly dosing; most commonly prescribed dose; for treatment of postmenopausal osteoporosis in women and osteoporosis in men; take the same day every week
• Alendronate 70 mg effervescent tablet — dissolve in 4 oz plain water before drinking; same efficacy; option for patients who prefer liquid or have difficulty swallowing tablets
• Alendronate 70 mg/75 mL oral solution — liquid formulation; same fasting and upright position requirements apply

Critical administration instructions — MUST be followed:

1. Take on an empty stomach, first thing in the morning, immediately upon waking
2. Swallow with a full glass (6–8 fl oz) of plain water only — not coffee, juice, mineral water, or any other beverage
3. Remain fully upright (sitting, standing, or walking) for at least 30 minutes after taking — do not lie down
4. Take nothing else by mouth (no food, drink, or other medications) for at least 30 minutes after taking alendronate
5. Do not take at bedtime or before rising for the day
6. Patients who cannot comply with these requirements should not use alendronate

Price of Fosamax and Generic Alendronate

Generic alendronate is widely available at very low cost through pharmacy discount programmes. The brand-name Fosamax is significantly more expensive. Both 35 mg weekly and 70 mg weekly generic forms are routinely available for a few dollars per month. Prescription coverage is almost universal. Calcium and vitamin D supplements, required alongside therapy, are OTC and inexpensive.

Frequently Asked Questions

What are atypical femoral fractures and how common are they?

Atypical femoral fractures (AFFs) are stress fractures that occur in the subtrochanteric region or diaphysis of the femur — a site atypical of the typical osteoporotic femoral neck fractures. They are associated with prolonged bisphosphonate use (typically >5 years) and are thought to result from over-suppression of bone turnover that prevents normal remodelling from repairing micro-damage. They typically occur with minimal or no trauma. The absolute risk remains low — approximately 3–50 per 100,000 patient-years at 5–10 years — and is far outweighed by the hip fractures prevented during the first 5 years of treatment in high-risk patients. After 5 years, physicians may recommend a "drug holiday" of 1–3 years for lower-risk patients while maintaining benefits from bone-stored alendronate.

What is osteonecrosis of the jaw and who is at risk?

Osteonecrosis of the jaw (ONJ) — also called bisphosphonate-related osteonecrosis of the jaw (BRONJ) — is a rare complication characterised by exposed, non-healing bone in the jaw. Risk is strongly correlated with IV bisphosphonate use in oncology patients (much higher doses than osteoporosis treatment) and dental procedures (extractions, implants) that disrupt oral mucosa. In patients taking oral alendronate for osteoporosis, ONJ risk is estimated at approximately 1:10,000 to 1:100,000 — far lower than IV bisphosphonate users. Good oral hygiene and regular dental care are recommended; patients should inform their dentist of bisphosphonate use. There is no clear benefit to stopping oral bisphosphonates before routine dental procedures for osteoporosis-dose patients.

Can alendronate be taken with calcium supplements?

No — not simultaneously. Calcium, magnesium, dairy products, antacids, iron, and vitamins containing divalent cations all chelate alendronate in the GI tract, forming insoluble complexes that cannot be absorbed. Since alendronate's bioavailability is already extremely low (<1%), even a small reduction in absorption can eliminate efficacy entirely. Calcium supplements, vitamins, and other medications must be taken at least 30 minutes after alendronate — and many physicians recommend taking calcium at a completely different time of day (e.g. with lunch) to eliminate any risk of interaction. Adequate calcium intake (1,000–1,200 mg elemental calcium/day from all sources) and vitamin D (800–1,000 IU/day) are required alongside alendronate for optimal efficacy; they just cannot be taken at the same time.

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