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National Osteoporosis Society

Osteoporosis helpline

0845 450 0230

9am - 5pm Mon-Fri

Alendronic Acid

Alendronic acid, or alendronate, is one of the most commonly prescribed drugs to treat osteoporosis. It is one of a family of drugs called bisphosphonates and is often known by its brand name Fosamax.

How it works.

Our bones are continuously maintained by our bodies to keep them healthy. We have cells that break down old bone (osteoclasts) and cells that rebuild with new bone (osteoblasts). These cells completely renew our entire skeleton about every seven years. Alendronic acid, like all bisphosphonates, slows down this process. It inhibits the osteoclasts from breaking down the old bone too quickly and gives the osteoblasts a chance to rebuild more effectively. This improves the density of the bones and reduces the risk of fractures.

How it’s taken.

Alendronic acid, either as generic alendronate or brand-named Fosamax, is taken as a tablet. It usually comes as a 70mg weekly tablet but a daily 10mg tablet can sometimes be prescribed. The company that make Fosamax also make a tablet called Fosavance which combines 70mg of alendronic acid with 2800 IU of vitamin D3.

Alendronic acid must be taken on an empty stomach otherwise it will not be effective. You should take it first thing in the morning and not eat or drink anything other than water for at least 30 minutes afterwards. During this time you should remain upright, don’t be tempted to go back to bed!

Possible side effects of alendronic acid.

People taking alendronic acid sometimes get an inflamed food pipe (oesophagus), a sore throat and difficulty swallowing, or aching muscles and bones. Chest pains or worsening heartburn should be reported to your doctor.

For more information about alendronic acid and other drugs:

Rare side effects.

Osteonecrosis of the jaw, or ONJ

In a very small number cases (fewer than 1 in 10,000) bisphosphonates like alendronic acid have been linked to osteonecrosis of the jaw. Osteonecrosis means some of the cells die in the affected bone. In the jawbone it can make recovering from invasive dental surgery like tooth extractions take longer than usual.

Unusual (or ‘atypical’) thigh bone fractures

Stress fractures of the middle or top of the femur (thigh bone) have been reported in a small number of patients treated with alendronate (alendronic acid) tablets for osteoporosis. Most of those affected had been taking alendronate for at least three years. The fractures occurred after little or no force and in many cases there was a history of pain at the site of fracture, the thigh, for a few weeks or months. In some cases the fractures affected both sides and they were often slow to heal. In most cases, the fractures healed after alendronate was discontinued.

More information about rare side effects like osteonecrosis of the jaw and unusual thigh bone fractures:

If you are currently taking alendronic acid and are worried about side effects, call our Helpline on 0845 450 0230


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Related links

Scottish Dental Clinical Effectiveness Programme

Oral Health Management of Patients Proscribed Bisphosphonates

Link also contains a patient advice leaflet.

Almost three million people in the UK are estimated to have osteoporosis

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