Alendronate: Uses, Dosage & Side Effects
A bisphosphonate medication that prevents and treats osteoporosis by inhibiting bone resorption and reducing fracture risk
Alendronate (alendronic acid) is a bisphosphonate medication widely prescribed to treat and prevent osteoporosis in postmenopausal women. It works by inhibiting osteoclast-mediated bone resorption, helping to rebuild bone and significantly reducing the risk of fractures in the spine, hip, and wrist. Alendronate is included on the WHO Model List of Essential Medicines and is one of the most extensively studied osteoporosis treatments, with clinical trials demonstrating fracture risk reductions of up to 50%. It requires careful administration — taken on an empty stomach with plain water while remaining upright — to ensure proper absorption and to minimize the risk of esophageal irritation.
Quick Facts: Alendronate
Key Takeaways
- Alendronate is a first-line bisphosphonate for treating and preventing postmenopausal osteoporosis, reducing vertebral and hip fracture risk by 35–50%.
- The weekly 70 mg dose is as effective as the daily 10 mg dose and is preferred for better adherence and fewer gastrointestinal side effects.
- Must be taken on an empty stomach with a full glass of plain tap water, followed by remaining upright for at least 30 minutes before eating or drinking.
- Rare but serious risks include osteonecrosis of the jaw (ONJ), atypical femur fractures, and esophageal ulceration — dental evaluation is recommended before starting treatment.
- Treatment duration is typically 3–5 years, after which a “drug holiday” may be considered depending on individual fracture risk.
What Is Alendronate and What Is It Used For?
Alendronate belongs to a group of non-hormonal medications called bisphosphonates. These drugs work by binding to the mineral surface of bone and inhibiting the activity of osteoclasts — the cells responsible for breaking down bone tissue. By slowing bone resorption, alendronate allows the bone-building cells (osteoblasts) to work more effectively, resulting in a net gain of bone mass over time.
The primary indication for alendronate is postmenopausal osteoporosis. Osteoporosis is a condition characterized by reduced bone density and deterioration of bone tissue, making bones fragile and more susceptible to fractures. After menopause, the ovaries stop producing estrogen, a hormone that plays a critical role in maintaining bone health. The resulting decline in estrogen levels accelerates bone loss, increasing the risk of osteoporosis significantly. The condition often develops silently, without symptoms, until a fracture occurs.
Clinical trials have demonstrated that alendronate treatment reduces the risk of vertebral fractures by approximately 47% and hip fractures by approximately 51% over three years in women with established osteoporosis (Fracture Intervention Trial, JAMA 1998). These landmark findings established alendronate as one of the most effective treatments for osteoporosis prevention and formed the basis for its inclusion in most national and international treatment guidelines.
Beyond postmenopausal osteoporosis, alendronate may also be prescribed for:
- Osteoporosis in men — to increase bone mass and reduce fracture risk
- Glucocorticoid-induced osteoporosis — in patients taking long-term corticosteroid therapy (such as prednisolone)
- Paget’s disease of bone — a condition causing abnormal bone remodeling (at different dosing)
In addition to pharmacological treatment, healthcare providers typically recommend lifestyle modifications to support bone health. These include regular weight-bearing exercise, adequate calcium and vitamin D intake, smoking cessation, and fall prevention strategies. Alendronate works best as part of a comprehensive osteoporosis management plan that addresses both medical and lifestyle factors.
What Should You Know Before Taking Alendronate?
Alendronate is not suitable for everyone. Before starting treatment, your healthcare provider will evaluate your medical history, current medications, and overall health to determine whether this medication is appropriate for you. It is important to have an open discussion about any existing health conditions, as several factors can influence whether alendronate is safe and effective for your situation.
Contraindications
You should not take alendronate if any of the following apply:
- You are allergic to alendronic acid or any of the other ingredients in the tablet (microcrystalline cellulose, crospovidone, magnesium stearate)
- You have esophageal abnormalities such as stricture (narrowing) or achalasia (inability of the esophagus to move food to the stomach)
- You are unable to stand or sit upright for at least 30 minutes after taking the tablet
- You have low blood calcium levels (hypocalcemia) — this must be corrected before starting alendronate
- You have severe kidney impairment (creatinine clearance below 35 ml/min)
Warnings and Precautions
Talk to your doctor or pharmacist before taking alendronate if any of the following conditions apply to you:
- Kidney problems — alendronate is not recommended for patients with severe renal impairment
- Swallowing or digestive problems — including Barrett’s esophagus, difficulty swallowing, or active upper gastrointestinal disease
- Low calcium levels — hypocalcemia must be treated before starting alendronate
- Malabsorption syndrome — conditions affecting mineral absorption in the stomach or intestines
- Vitamin D deficiency — should be corrected before and maintained during treatment
Consider having a dental examination before starting alendronate treatment, particularly if you have cancer, are undergoing chemotherapy or radiotherapy, are taking corticosteroids, have poor dental health, or are a smoker. Osteonecrosis of the jaw (ONJ) — a rare condition involving bone damage in the jaw — has been reported in patients taking bisphosphonates. Maintain good oral hygiene and attend regular dental check-ups during treatment. Inform your dentist that you are taking alendronate before any dental procedures, especially tooth extractions.
Irritation, inflammation, or ulceration of the esophagus (the tube connecting the mouth to the stomach) can occur with alendronate use, particularly if patients do not drink a full glass of water with the tablet or lie down within 30 minutes of taking it. These side effects can worsen if the patient continues taking alendronate after symptoms develop. Stop taking alendronate and contact your doctor immediately if you experience difficulty swallowing, pain on swallowing, chest pain, or new or worsening heartburn.
Pregnancy and Breastfeeding
Alendronate is intended for use in postmenopausal women and should not be taken during pregnancy or breastfeeding. In animal studies, bisphosphonates have been shown to cross the placenta, and the effects on the human fetus are not well established. If you become pregnant while taking alendronate, stop the medication immediately and consult your healthcare provider. Because bisphosphonates bind to bone matrix and are released slowly over years, women of childbearing potential should be counseled about the potential risks before starting treatment.
Children and Adolescents
Alendronate is not recommended for children and adolescents under 18 years of age. The safety and efficacy of alendronate in pediatric populations have not been established, and the effects on growing bone are unknown.
Driving and Using Machines
Alendronate may cause side effects such as blurred vision, dizziness, or severe bone, muscle, or joint pain that could impair your ability to drive or operate machinery. Individual responses to the medication vary. If you experience any of these effects, do not drive or use machines until the symptoms resolve.
How Does Alendronate Interact with Other Drugs?
Drug interactions can significantly affect how well alendronate works or increase the risk of side effects. The most clinically important interaction involves substances that interfere with the already low oral bioavailability of alendronate (approximately 0.6–0.7% under fasting conditions). Any food, drink (other than plain tap water), or medication taken at the same time can virtually eliminate absorption of the drug.
It is essential to inform your doctor or pharmacist about all medications you are taking, including prescription drugs, over-the-counter medicines, herbal supplements, and vitamins. Below is a summary of the most important interactions:
Major Interactions
| Interacting Drug | Effect | Recommendation |
|---|---|---|
| Calcium supplements | Significantly reduces alendronate absorption by forming insoluble complexes | Take calcium at least 30 minutes after alendronate (preferably with lunch or dinner) |
| Antacids (e.g., aluminum, magnesium hydroxide) | Substantially reduces alendronate absorption | Wait at least 30 minutes after alendronate before taking antacids |
| Iron supplements | May reduce alendronate absorption | Take iron supplements at a different time of day |
| NSAIDs (e.g., ibuprofen, naproxen, aspirin) | Increases risk of gastrointestinal irritation, ulceration, and bleeding | Use with caution; discuss with your doctor if you need regular NSAID use |
| Corticosteroids (e.g., prednisolone, dexamethasone) | May increase risk of GI side effects; corticosteroids also worsen bone loss | Combined use may be appropriate under medical supervision to prevent glucocorticoid-induced osteoporosis |
Minor Interactions
Proton pump inhibitors (PPIs) such as omeprazole and pantoprazole may theoretically reduce alendronate absorption due to changes in gastric pH. However, clinical studies have not shown a significant reduction in alendronate efficacy when used concurrently. Nevertheless, some observational data suggest that long-term PPI use may independently increase fracture risk, which should be considered when both medications are used together.
Hormone replacement therapy (HRT) can be used alongside alendronate. Some studies suggest that the combination may provide additional benefits for bone mineral density beyond either treatment alone, though this combination is not routinely recommended in current guidelines.
After swallowing your alendronate tablet, wait at least 30 minutes before taking any other medication for the day, including vitamins, supplements, antacids, and calcium. Alendronate is only effective when taken on an empty stomach. This timing requirement is essential for proper drug absorption and cannot be overlooked.
What Is the Correct Dosage of Alendronate?
Always take alendronate exactly as prescribed by your doctor. The dosage depends on the specific condition being treated and your individual clinical situation. Do not change your dose without consulting your healthcare provider.
Adults
Postmenopausal Osteoporosis (Treatment and Prevention)
Preferred: 70 mg once weekly — take one tablet on the same day each week.
Alternative: 10 mg once daily (the weekly formulation is generally preferred for better adherence).
Both dosing regimens have demonstrated equivalent efficacy in clinical trials. The once-weekly 70 mg dose produces the same total weekly exposure to alendronate as the daily 10 mg dose, with comparable improvements in bone mineral density and fracture risk reduction.
Osteoporosis in Men
Dose: 70 mg once weekly or 10 mg once daily, following the same administration instructions as for postmenopausal osteoporosis.
Glucocorticoid-Induced Osteoporosis
Dose: 5 mg once daily for patients not receiving estrogen therapy, or 10 mg once daily in some treatment protocols. Consult your physician for the appropriate dose based on your specific situation.
How to Take Alendronate Correctly
The way you take alendronate is critically important for both effectiveness and safety. Following these instructions carefully will help the medication reach your stomach quickly and reduce the risk of esophageal irritation:
- Choose your day: Select the day of the week that best fits your schedule. Take your tablet on the same day each week.
- Take it first thing in the morning: After waking up and before eating, drinking, or taking any other medication, swallow the tablet whole with a full glass of plain tap water (at least 200 ml / 7 fl oz).
- Do not use mineral water (still or sparkling), coffee, tea, juice, or milk — these can reduce absorption.
- Do not chew, crush, or dissolve the tablet — swallow it whole to avoid mouth ulcers.
- Stay upright for 30 minutes: After swallowing the tablet, remain sitting or standing for at least 30 minutes. Do not lie down during this time.
- Wait before eating or taking other medicines: Do not eat, drink, or take any other medication (including antacids, calcium, and vitamins) for at least 30 minutes after taking alendronate.
- Do not take at bedtime or before getting up for the day.
Children
Alendronate should not be given to children and adolescents under 18 years of age. Safety and efficacy have not been established in this population.
Missed Dose
If you forget to take your weekly dose, take one tablet the morning after you remember. Do not take a double dose to make up for a forgotten tablet. Return to your regular schedule by taking one tablet on your usual chosen day of the week.
Overdose
If you accidentally take too many alendronate tablets, drink a full glass of milk and contact a doctor or poison control center immediately. Do not induce vomiting and do not lie down. Overdose may cause low blood calcium (hypocalcemia), low blood phosphate, and upper gastrointestinal adverse events such as stomach upset, heartburn, esophagitis, gastritis, or ulcer.
What Are the Side Effects of Alendronate?
Like all medicines, alendronate can cause side effects, although not everyone gets them. Most side effects are mild to moderate and can be significantly reduced by taking the medication correctly as described in the dosage section. However, some side effects can be serious and require immediate medical attention.
- Difficulty swallowing or pain when swallowing
- Chest pain or new/worsening heartburn
- Severe allergic reactions (hives, swelling of face, lips, tongue, or throat, difficulty breathing)
- Pain in the mouth, jaw, or teeth; jaw swelling or numbness; loose teeth
- Pain, weakness, or discomfort in the thigh, hip, or groin (may indicate an atypical fracture)
Side Effect Frequency
Very Common
- Bone, muscle, and/or joint pain (sometimes severe)
Common
- Heartburn, difficulty swallowing, pain on swallowing
- Esophageal ulcers (may cause chest pain or heartburn)
- Abdominal pain, stomach discomfort, belching after meals
- Constipation, feeling of fullness, diarrhea, flatulence
- Joint swelling
- Hair loss, itching
- Headache, dizziness
- Fatigue, swelling of hands or feet
Uncommon
- Nausea, vomiting
- Irritation or inflammation of the esophagus or stomach
- Black or tarry stools
- Blurred vision, eye pain, redness of the eye
- Skin rash, skin redness
- Transient flu-like symptoms (muscle aches, malaise, sometimes fever) — typically at the start of treatment
- Taste disturbances
Rare
- Allergic reactions including urticaria, angioedema (swelling of face, lips, tongue, and/or throat that may cause breathing or swallowing difficulties), severe skin reactions
- Osteonecrosis of the jaw (ONJ) — pain, swelling, sores in the mouth, numbness or heaviness in the jaw, or loose teeth
- Atypical femoral fractures — unusual fractures of the thigh bone, particularly in patients on long-term treatment
- Symptoms of low blood calcium (muscle cramps, spasms, tingling in fingers or around the mouth)
- Stomach or peptic ulcer (sometimes severe, with bleeding)
- Esophageal stricture (narrowing)
- Mouth ulcers (if tablet was chewed or sucked)
- Rash worsened by sunlight
Very Rare
- Osteonecrosis of the ear canal — ear pain, discharge, or infection
If any side effects become severe or you experience symptoms not listed here, contact your doctor or pharmacist. It can be helpful to keep a record of any side effects you experience, including when they started and how long they lasted, to share with your healthcare provider.
It is important to report suspected side effects after a medicine has been authorized. This helps to continuously monitor the benefit-risk balance of the medicine. You can report side effects to your national pharmacovigilance authority (e.g., the FDA in the United States via MedWatch, or the EMA in the European Union).
How Should You Store Alendronate?
Proper storage of alendronate helps ensure the medication remains effective and safe throughout its shelf life. Follow these guidelines:
- Keep out of sight and reach of children — store in a secure location.
- No special storage conditions are required — store at room temperature, away from excessive heat and moisture.
- Keep in the original packaging — the blister pack protects the tablets from moisture and light.
- Check the expiration date — do not use after the date printed on the carton and blister pack after “EXP”. The expiration date refers to the last day of that month.
- Do not dispose of medications in wastewater or household waste — return unused or expired medicines to a pharmacy for proper disposal. This helps protect the environment.
What Does Alendronate Contain?
Active Ingredient
The active substance is alendronic acid. Each tablet contains 70 mg of alendronic acid, equivalent to 91.37 mg of sodium alendronate trihydrate. Alendronic acid is a nitrogen-containing bisphosphonate that acts specifically on bone tissue by inhibiting osteoclast-mediated bone resorption.
Inactive Ingredients (Excipients)
The other ingredients are:
- Microcrystalline cellulose — a commonly used filler and binder in pharmaceutical tablets
- Crospovidone — a disintegrant that helps the tablet break down in the stomach
- Magnesium stearate — a lubricant that prevents the tablet from sticking during manufacture
Appearance
Each tablet is white, oval, flat, and embossed with “70” on one side. Alendronate is available in blister packs containing 2, 4, 8, 12, or 40 tablets. Not all pack sizes may be marketed in every country.
This medicine contains less than 1 mmol (23 mg) sodium per tablet, meaning it is essentially sodium-free. This is relevant for patients on sodium-restricted diets.
Frequently Asked Questions About Alendronate
Medical References
All medical information on this page is based on the following peer-reviewed sources and international guidelines:
- European Medicines Agency (EMA). "Alendronate – Summary of Product Characteristics (SmPC)." EMA European regulatory guidance on alendronate prescribing and safety.
- U.S. Food and Drug Administration (FDA). "Fosamax (Alendronate Sodium) – Prescribing Information." FDA Label FDA-approved prescribing information and safety data.
- Black DM, et al. (1996). "Randomised trial of effect of alendronate on risk of fracture in women with existing vertebral fractures." The Lancet. 348(9041):1535–1541. doi:10.1016/S0140-6736(96)07088-2 Fracture Intervention Trial (FIT) – landmark RCT establishing alendronate efficacy. Evidence level: 1A
- National Institute for Health and Care Excellence (NICE). "Bisphosphonates for treating osteoporosis." Technology Appraisal TA464. NICE TA464 UK clinical guidelines for bisphosphonate use in osteoporosis.
- World Health Organization (WHO). "Model List of Essential Medicines – 23rd List (2023)." WHO Essential Medicines Alendronate is included on the WHO Model List of Essential Medicines.
- Camacho PM, et al. (2020). "American Association of Clinical Endocrinologists/American College of Endocrinology Clinical Practice Guidelines for the Diagnosis and Treatment of Postmenopausal Osteoporosis." Endocrine Practice. 26(Suppl 1):1–46. US clinical practice guidelines for osteoporosis management.
- Wells GA, et al. (2008). "Alendronate for the primary and secondary prevention of osteoporotic fractures in postmenopausal women." Cochrane Database of Systematic Reviews. doi:10.1002/14651858.CD001155.pub2 Cochrane systematic review of alendronate efficacy and safety. Evidence level: 1A
Evidence grading: This article uses the GRADE framework (Grading of Recommendations Assessment, Development and Evaluation) for evidence-based medicine. Evidence level 1A represents the highest quality of evidence, based on systematic reviews of randomized controlled trials.
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