Key messages

• Alendronate used for up to five years may prevent spinal fractures in women who are at lower risk for fractures, or in those who have not yet had a fracture of the spine.

• Alendronate used for up to three years in women diagnosed with osteoporosis, with low bone density, or who have already had a fracture of the spine, probably prevents fractures of the spine.

What is osteoporosis?

Osteoporosis is a disease which makes bones weak and fragile. Bone is living tissue that is constantly being broken down and replaced. In osteoporosis, old bone breaks down faster than new bone can replace it. As this happens, the bones lose minerals (such as calcium). This makes bones more likely to break even after a minor injury, such as a bump or fall. Women are more likely to get osteoporosis after menopause.

What is alendronate?

Alendronate is a bisphosphonate, a type of medicine which slows down the cells that break down the old bone.

What did we want to find out?

We aimed to find out if alendronate is better than placebo (an inactive or 'dummy' medicine) or other medicines in preventing or reducing fractures in postmenopausal women.

What did we do?

We searched for studies that compared alendronate with placebo or other anti-osteoporotic medicines for osteoporosis in postmenopausal women. We compared and summarized the results of the studies and rated our confidence in the evidence, based on factors such as study methods and sizes.

What did we find?

We found 119 eligible studies. Of these, 102 studies provided usable data, and 40 studies compared alendronate to placebo (dummy pill).

Key findings

In women who are at a lower risk for fractures because they have bone density closer to normal, or they may not yet have a fracture in the bones of their spine, alendronate used for up to five years:

• may prevent clinical spinal fractures – that is, fractures indicated by clinical signs and symptoms, without radiographic evidence;

• may prevent fractures in bones other than the spine. However, specifically in hip and wrist fractures, alendronate may make no difference;

• may make no difference to the number of women who withdrew from the study due to adverse events – that is, unwanted, harmful events;

• may make no difference to the number of women experiencing serious adverse events.

In women who are at a higher risk for fractures because they have already been diagnosed with osteoporosis, have low bone density, or have already had a spinal fracture, alendronate used for up to three years:

• probably prevents clinical spinal fractures;

• may prevent fractures in bones other than the spine;

• may prevent hip and wrist fractures;

• may reduce serious adverse events;

We do not know if alendronate reduces withdrawals due to adverse events in this group of women.

The best estimates for women at lower fracture risk taking alendronate or placebo are as follows.

• For clinical spinal fractures, evidence suggests that if 3 out of 100 women taking placebo experience a fracture, only 1 out of 100 women taking alendronate will.

• If 10 out of 100 women on placebo have a fracture in bones other than the spine, only 8 out of 100 on alendronate are likely to.

• For hip and wrist fractures, there may be no difference between the two groups in the number of women experiencing fractures.

The best estimates for women at higher fracture risk taking alendronate or placebo are as follows.

• If 5 out of 100 women on placebo have a clinical spinal fracture, only 2 out of 100 women on alendronate are likely to.

• If 14 out of 100 women on placebo have a fracture in bones other than the spine, only 11 out of 100 on alendronate are likely to.

• If 2 out of 100 women on placebo have a hip fracture, only 1 out of 100 on alendronate are likely to.

• If 4 out of 100 women on placebo have a wrist fracture, only 2 out of 100 on alendronate are likely to.

What are the limitations of the evidence?

For most findings, our confidence in the evidence was low, because it is possible that the women in the studies, and the researchers assessing outcomes, were aware of which treatment the women received. Additionally, some of the evidence focused on specific alendronate doses, whereas the question we wanted to answer was broader. Finally, for some fracture outcomes, the evidence was based on few cases.

How current is the evidence?

The evidence is current to 1 February 2023. This is an update of a Cochrane review originally published in 2008.