How Do Osteoporosis Drugs Like Alendronate Work, and What Are Their Risks?

Alendronate (Fosamax) is an oral bisphosphonate used to treat osteoporosis. It slows bone breakdown, which can help protect against fractures. Common alendronate side effects involve the esophagus and stomach, and rare serious problems include jaw and thigh bone complications. This article explains how alendronate works, how it is taken, what the main risks are, how other bone medicines differ, and which symptoms need urgent care.

How alendronate works on bone

Bone is living tissue. Throughout adult life, cells called osteoclasts break down old bone while cells called osteoblasts build new bone. After menopause, and with aging, breakdown can outpace rebuilding. Bones become thinner and more fragile, which is the pattern described as osteoporosis. MedlinePlus (NIH) gives an overview of the condition on its Osteoporosis page.

Alendronate belongs to the bisphosphonate class. The drug attaches to bone surfaces, and osteoclasts take it up when they start breaking bone down. That interferes with how those cells work and shortens their activity. Bone building continues, so the balance can shift toward stronger bone over time. Several factors contribute to the overall effect, and the exact details are still being studied.

Alendronate does not rebuild bone the way some injectable medicines do. It mainly slows loss and allows some gain in density. Outcomes vary from person to person.

What the evidence says about fracture prevention

A review of randomized trials, Alendronate for the primary and secondary prevention of osteoporotic fractures in postmenopausal women, examined whether alendronate lowers fracture risk. The review reports that alendronate can reduce the chance of fractures in postmenopausal women. How much it helps depends on a person's starting fracture risk, which is why clinicians weigh your history, bone density results and other risk factors before recommending a drug.

Bone density testing is one tool used for this decision. MedlinePlus explains the scan on its Bone Density page. Clinicians combine your scan, age, prior fractures, medications and other health conditions, often using a fracture-risk calculator such as FRAX, rather than relying on one number.

Who may be offered alendronate

Alendronate is often considered for postmenopausal women with osteoporosis or a high fracture risk. It is also used in some men and in people taking long-term corticosteroids, depending on the situation. Your clinician decides whether a bisphosphonate is appropriate based on your overall risk and other conditions.

Calcium and vitamin D are usually part of the plan, since bone needs both. Our article on taking vitamin D and calcium together covers that question, so this page does not repeat it.

How alendronate is taken, and why the routine matters

Alendronate comes as a daily or weekly tablet, and an oral solution exists. The body absorbs very little of it, and food, coffee, juice and many supplements can reduce absorption further. It can also irritate the esophagus if it lingers there. For these reasons the product's prescribing instructions generally direct people to follow a specific routine:

• Take it first thing in the morning on an empty stomach.
• Swallow it with a full glass of plain water, not coffee, juice or mineral water.
• Stay upright, sitting or standing, for at least 30 minutes afterward, and do not lie back down.
• Wait at least 30 minutes before eating, drinking anything else or taking other medicines, including calcium.
• Do not chew or suck on the tablet.

Check the exact instructions on your prescription label, and ask your prescriber or pharmacist if you are unsure. If you miss a dose, do not change the schedule on your own; ask your pharmacist what the label says for your product. A review of an alternative formulation, Alendronate sodium hydrate (oral jelly), describes options studied for people who find tablets hard to swallow. Ask your clinician whether any alternative is appropriate for you.

Alendronate side effects and warnings

The most frequent problems involve the digestive tract. They can include heartburn, stomach pain, nausea, constipation or diarrhea, and pain when swallowing. Some people also notice bone, joint or muscle aches. Many of these are linked to how the pill passes through the esophagus, which is why the upright routine matters.

Before you start alendronate, tell your prescriber about any swallowing problems, esophageal disease such as a narrowing (stricture) or a condition that slows emptying of the esophagus (achalasia), low blood calcium, or kidney disease. The product's prescribing information lists these as reasons alendronate may not be appropriate. It also advises against use in people who cannot stay upright for 30 minutes, and cautions against use when kidney function is substantially reduced; your prescriber can tell you where your own kidney function falls. Low blood calcium and vitamin D status are generally corrected before treatment begins, under your prescriber's direction. If you already take an acid-reducing medicine, the question of how it fits with your bone treatment is one to raise with your prescriber; our article on omeprazole and other PPIs gives background on that drug class.

Less common but serious risks

Esophageal injury

Pills that stick in the esophagus can cause inflammation or ulcers. New chest pain, pain on swallowing, or heartburn that is new or worsening may suggest this. Severe chest pain, or chest pain with shortness of breath, sweating or spread to the arm or jaw, needs emergency care because it can have a cardiac cause. For milder new pain on swallowing or heartburn, contact your prescriber the same day. Do not keep taking tablets through new swallowing pain or chest pain; your prescriber decides whether to hold the drug while it is evaluated.

Osteonecrosis of the jaw

Osteonecrosis of the jaw is an area of exposed jaw bone that fails to heal. It is much less common in people taking osteoporosis doses than in people receiving high-dose bisphosphonates for cancer. Risk is associated with invasive dental work, poor oral health and other factors. Tell your dentist you take a bisphosphonate, and report jaw pain, swelling, loose teeth or slow healing after dental work to your dentist or clinician.

Unusual thigh bone fractures

Atypical femur fractures are unusual breaks in the thigh bone, sometimes after little or no trauma. They are much less common than the ordinary osteoporotic fractures that bisphosphonates help prevent, and a single symptom does not establish one. Dull or aching pain in the groin, hip or thigh, especially if it lasts for weeks, deserves an evaluation, which may include imaging. Risk appears to be associated with longer duration of use.

Low calcium and kidney concerns

Alendronate can lower blood calcium, which is one reason low calcium should be corrected before starting. Mild muscle cramps or tingling around the mouth or in the fingers can be signs of low calcium and call for a same-day call to your clinician. Seizure, severe muscle spasms, or confusion with muscle cramps need emergency care. Clinicians may check kidney function before and during treatment.

Allergic reaction

As with any medicine, a serious allergic reaction is possible, though uncommon. Swelling of the face, lips or tongue, trouble breathing, or widespread hives are emergencies.

How long people stay on a bisphosphonate

Because some risks, such as atypical thigh fractures, are associated with longer use, clinicians often review treatment after several years and decide whether to continue, pause or switch. This decision depends on your fracture history and bone density. Bisphosphonates stay in bone for a long time, so some protection may persist for a while after stopping. Do not stop or restart alendronate on your own; this is a decision to make with your prescriber.

How other osteoporosis medicines differ

• Other bisphosphonates: risedronate and ibandronate are oral options, and zoledronic acid is given by infusion. They share the same general class risks.
• Denosumab: an injection that also slows bone breakdown through a different mechanism. Stopping it can be followed by rapid bone loss and fractures, so any plan to stop it should be made with a clinician. Its labeling also carries a boxed warning about severe low calcium in people with advanced kidney disease, so ask your prescriber how it applies to you.
• Anabolic (bone-building) drugs: teriparatide, abaloparatide and romosozumab stimulate bone formation and are often reserved for higher-risk people. Romosozumab, an anti-sclerostin antibody, is reviewed in a meta-analysis of anti-sclerostin therapy. Its labeling carries a boxed warning about heart attack, stroke and cardiovascular death, so your clinician will weigh your heart history.
• Hormone therapy: estrogen-based treatment can affect bone but has its own risks and benefits; our article on menopausal hormone therapy covers that discussion.

The right choice depends on your fracture risk, kidney function, swallowing, other conditions and preferences. Cost and insurance coverage can also shape what is practical.

Supplements and food: what to tell your clinician

Some small studies have explored adding supplements such as curcumin to alendronate, for example this trial of curcumin with alendronate. Findings from small studies do not establish that a supplement helps, and some products can interfere with absorption. Tell your clinician and pharmacist about every supplement you take.

Questions to bring to your appointment

• What is my fracture risk, and how was it estimated?
• Is alendronate or another medicine a better fit given my stomach, swallowing and kidneys?
• Do I need a dental check before starting?
• How will we monitor bone density and decide how long to continue?
• Do my other medicines or supplements affect absorption?

For recovery after a break, see our article on recovery after a hip fracture, and for warning signs that precede a fracture, see early signs of osteoporosis.

When to Seek Medical Care