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Fosamax: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on March 31, 2023.

1. How it works

  • Fosamax is a brand (trade) name for alendronate which may be used for the treatment or prevention of osteoporosis.
  • Fosamax (alendronate) works by inhibiting osteoclasts which are responsible for breaking down and reabsorbing bone (by a process known as bone resorption). Alendronate strengthens bones by slowing down bone loss and allowing osteoblasts (bone-building cells) to work more effectively, improving bone mass.
  • Fosamax belongs to a group of medicines known as bisphosphonates.

2. Upsides

  • Fosamax is used in the treatment and prevention of osteoporosis in postmenopausal women and men.
  • Fosamax may also be used to treat glucocorticoid-induced osteoporosis and Paget's disease of the bone.
  • Fosamax may also be used to treat adverse skeletal effects caused by some cancers.
  • Some studies have shown that Fosamax may be more effective than other bisphosphonates such as risedronate at increasing bone mineral density and reducing bone turnover without a higher risk of side effects.
  • Strengthens bones.
  • Depending on the condition being treated and the dosage used, Fosamax may be taken once daily or once weekly.
  • Fosamax is available as a generic under the name alendronate. Alendronate tablets are available in a wider range of strengths (Fosamax is only available as a 70mg tablet).

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Abdominal pain, bone muscle or joint pain, dyspepsia, hair loss, itch, constipation, diarrhea, flatulence, dizziness, headache, vertigo, and swelling of the ankles or feet are the most common side effects.
  • Fosamax, like other bisphosphonates, may irritate the esophagus and stomach. Some cases have been severe enough to warrant hospitalization. The risk is greater in people who lie down soon after taking Fosamax or who don't take it with a full glass of water. Take exactly as directed. Fosamax should be taken with a full glass of water and the person taking Fosamax should remain upright for at least 30 minutes after taking it.
  • Severe bone, joint, or muscle pain, necessitating discontinuation of Fosamax in some people, has been reported, occurring from one day to several months after starting the drug.
  • Rarely may cause other side effects including uveitis (eye inflammation).
  • May not be suitable for some people including those with kidney disease, pre-existing esophageal conditions, low blood calcium levels (hypocalcemia), or who are unable to stand or sit upright for at least 30 minutes.
  • There are concerns about the long-term safety of bisphosphonates (such as Fosamax) as long-term use has been associated with atypical femur fractures, osteonecrosis of the jaw, and esophageal cancer.
  • Fracture risk reduction may also persist for years after treatment has stopped. The optimal duration of therapy with Fosamax has not been established. Periodically re-evaluate the need for therapy. Discontinuation of therapy should be considered by doctors after 3 to 5 years in patients at low risk of fracture.
  • Fosamax may interact with antacids or supplements containing calcium or magnesium.
  • Fosamax may lower calcium levels in the blood. Pre-existing low blood calcium levels should be corrected before Fosamax administration.
  • Fosamax is only available as a 70mg tablet. This may limit the range of indications Fosamax can be used for. The liquid preparation of Fosamax has been discontinued.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Fosamax helps to reduce the risk of fracture in people with osteoporosis and some other bone conditions. Dosage instructions, including remaining upright for at least 30 minutes and taking with a full glass of water, must be strictly followed. The optimal length of therapy remains unknown.

5. Tips

  • Take Fosamax at least 30 minutes before eating or drinking any food or beverages (other than water), or taking any other medication, including calcium, antacids, or vitamins.
  • Take Fosamax with a full glass of water and remain upright for at least 30 minutes. Do not lie down. Do not substitute water with mineral water, coffee, soda, juice, or tea. Never take Fosamax at bedtime. Take Fosamax exactly as directed by your doctor. Do not increase or decrease the dosage without your doctor's advice.
  • Avoid eating, drinking (other than water), or taking other medications for 30 minutes after taking Fosamax.
  • You may need to take supplementary calcium or vitamin D if your dietary intake is inadequate. Your doctor will advise you about this. If you are taking supplemental calcium, iron, magnesium, or antacids, take them at a different time of day to Fosamax (for example at lunchtime), as they may interfere with the absorption of Fosamax. Note that mineral water may contain a higher concentration of calcium than tap or bottled water, and you should only drink it if your doctor has confirmed it is compatible with Fosamax.
  • Talk to both your dentist and doctor if you require dental surgery or tooth extraction and you have been on Fosamax long-term. They may advise discontinuation of Fosamax.
  • Tell your doctor if you experience any thigh or groin pain, muscle cramps or twitches, severe or debilitating muscle pain, eye inflammation, or any other adverse effects of concern while you are taking Fosamax.

6. Response and effectiveness

  • Fosamax starts to affect markers that reflect bone resorption within one month of treatment and reaches a plateau by three to six months. Effects remain stable following continued treatment for up to three years.
  • Food can significantly decrease the absorption of Fosamax.

7. Interactions

Medicines that interact with Fosamax may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Fosamax. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Fosamax include:

  • aluminum salts
  • amikacin
  • angiogenesis inhibitors, such as bevacizumab or everolimus
  • aspirin
  • calcium supplements
  • chemotherapy agents for cancer
  • diuretics, such as bumetanide and furosemide
  • hormone replacement therapy
  • iron salts
  • lithium
  • magnesium salts
  • NSAIDs, such as ibuprofen, diclofenac, and naproxen
  • olsalazine
  • oral steroids, such as dexamethasone, prednisone, and methylprednisone
  • sirolimus and tacrolimus
  • zinc salts.

Note that this list is not all-inclusive and includes only common medications that may interact with Fosamax. You should refer to the prescribing information for Fosamax for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Fosamax only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: March 31, 2023.