Alendronic acid

Nitrogen-containing bisphosphonate

ATC code: M05BA04

Updated 27 Jul 2026 · Methodology

Indications

Glucocorticoid-induced osteoporosis

First line

Oral bisphosphonates, including alendronate, are first-line for preventing and treating osteoporosis in patients on systemic glucocorticoids ( 2017, SEIOMM 2022). In the Saag RCT (NEJM 1998), alendronate raised spine and femoral-neck bone mineral density versus placebo during long-term glucocorticoid therapy, with fewer new vertebral fractures on continued follow-up. Treatment is considered at prednisone doses of 5 mg/day or more for over 3 months, or when bone density is already reduced. Dosing matches postmenopausal osteoporosis: 70 mg once weekly. Calcium and vitamin D are a required baseline.

Sources

ICD-10: M81.4 · ICD-11: FB83.13

Postmenopausal osteoporosis

First line

First-line for postmenopausal osteoporosis per AACE/ACE 2020 and SEIOMM 2022. Cuts vertebral fracture risk by 47% and hip fracture by 51% (FIT trial). Standard dose 70 mg weekly; alternative 10 mg daily. After 5 years, reassess the need to continue (drug holiday) – women without high fracture risk may take a 1–2-year break.

Also used in glucocorticoid-induced osteoporosis at prednisolone ≥7.5 mg/day long-term ( 2022, first-line).

Sources

ICD-10: M81.0 · ICD-11: FB83.11

Paget's disease of bone

Second line

Alendronate lowers Paget's disease activity: it normalizes alkaline phosphatase (an activity marker) and eases bone pain (Siris RCT, 1996). The indication is approved (AEMPS ficha técnica). The regimen differs from the osteoporosis one – 40 mg daily for 6 months. That said, the Endocrine Society 2014 guideline prefers zoledronic acid: a single infusion gives deeper, more durable remission, so oral alendronate stays a second-line alternative, mainly when intravenous therapy is not feasible or not wanted. Treatment targets symptomatic disease and asymptomatic disease at high complication risk by lesion site.

Sources

ICD-10: M88.9 · ICD-11: FB85.Z

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Anti-aging and longevity

Not recommended

Alendronic acid is a bisphosphonate. It is prescribed for osteoporosis with confirmed reduced bone mineral density (T-score below -2.5 or with fragility fractures) and for Paget's disease (NOGG 2021, AACE 2020 guidelines). In anti-aging communities, alendronate is prescribed for bone rejuvenation with normal bone density. No clinical studies of prophylactic use outside osteoporosis exist; with normal bone density, the benefit does not outweigh the risks. The drug has serious adverse effects: esophageal erosions and ulcers (requires intake with plenty of water in an upright position), osteonecrosis of the jaw (especially after dental procedures), and atypical femoral fractures on long-term use (over 5 years). If alendronate was prescribed outside confirmed osteoporosis, consider seeking a second opinion.

Sources

How to read tiers A–F

AStrong evidence – first or second line in international guidelines
BRecommended in selected cases
CStudy data contradict each other
DBenefit not proven, no documented harm
FDocumented harm, or risk without benefit

Mechanism of action

Incorporated into bone hydroxyapatite and taken up by osteoclasts during resorption. Inhibits farnesyl pyrophosphate synthase, disrupting post-translational protein modification and inducing osteoclast apoptosis. Bone resorption falls and mineralized bone mass rises. The effect persists for years – bone half-life exceeds 10 years.

Safety

Contraindications

Bisphosphonate hypersensitivity
Hypocalcemia
Esophageal abnormalities (achalasia, stricture) or inability to stay upright for 30 minutes
Severe renal impairment (eGFR under 35)
Pregnancy and lactation

Serious adverse effects

Severe esophagitis, erosions, and ulcers (with incorrect intake)
Osteonecrosis of the jaw (rare, higher risk around dental procedures)
Atypical femoral fracture (after 5 years)
Severe hypocalcemia
Allergic reactions

Common adverse effects

Abdominal pain, reflux, esophagitis
Muscle, bone, and joint pain
Headache
Mild hypocalcemia

Pregnancy: can you take Alendronic acid?

Bisphosphonates accumulate in the skeleton for years. Contraindicated in pregnancy. Reliable contraception is required if therapy is needed in women of reproductive age.

Breastfeeding: can you take Alendronic acid?

No data on milk excretion. Not used during lactation.

Calculate RID Full profile on NIH LactMed ↗

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Practical notes

Timing and administration

Take strictly on empty stomach immediately upon waking, with a glass of plain water (at least 200 mL). Do not lie down for 30–60 minutes – high esophagitis risk. Breakfast, other medications, calcium, and vitamin D should wait at least 30 minutes. Mineral water, coffee, tea, and juice reduce absorption and must not be used. All patients should also take calcium 1000–1200 mg and vitamin D 800–1000 IU daily. Check creatinine and calcium before start and if symptoms arise.

Common myths

Myth: «long-term bisphosphonates destroy bone.» Fact: atypical femoral fracture and osteonecrosis of the jaw risk rises after 5 years, but absolute rates are low (atypical fracture 1–2 per 10,000 patient-years). The benefit of preventing hundreds of typical fractures outweighs that risk. Myth: «calcium and vitamin D are unnecessary on a bisphosphonate.» Fact: without adequate calcium and vitamin D, bisphosphonate efficacy falls and the risk of hypocalcemia and secondary hyperparathyroidism rises.

Drug–drug interactions

3 pairs found. Sorted from critical to minor.

MajorCalcium (oral salts: carbonate, citrate, lactate, gluconate)Mineral supplements. Calcium

Mechanism

Oral bioavailability of alendronic acid is minimal to begin with, and anything reaching the stomach at the same time wipes it out. The label says so plainly: food, drinks including mineral water, calcium supplements and antacids interfere with absorption. The paradox is that both are prescribed together for the same osteoporosis.

Symptoms

Densitometry that fails to improve after 12–24 months, or a new vertebral fracture while the bisphosphonate is running.

Management

Alendronate is taken on rising with a glass of tap water, and at least 30 minutes must pass before any other oral intake, calcium included, per the label. Do not lie down during that window because of oesophagitis risk. Calcium and vitamin D remain necessary in osteoporosis: move them to midday or dinner rather than stopping them.

Sources

Pair details →Calcium (oral salts: carbonate, citrate, lactate, gluconate) →

ModerateIron oral (salts: sulfate, bisglycinate, fumarate, gluconate, polymaltose; heme iron polypeptide, lactoferrin)Oral iron preparations; antianaemic agents

Mechanism

Iron falls into the category of other oral medicines the label requires to be separated from alendronic acid. On top of that, iron's ideal schedule (fasting) collides head-on with the bisphosphonate, which occupies the same slot.

Symptoms

Ferritin that does not recover and flat densitometry: both treatments run at half strength because they compete for the same time slot.

Management

Alendronate keeps the fasting slot and iron moves to mid-morning or evening, with vitamin C and away from dairy. With weekly alendronate the conflict is solved by fixing one day for the bisphosphonate and shifting iron only on that morning.

Sources

Pair details →Iron oral (salts: sulfate, bisglycinate, fumarate, gluconate, polymaltose; heme iron polypeptide, lactoferrin) →

ModerateMagnesium (oral salts: citrate, glycinate, oxide, sulfate)Mineral supplements. Macrominerals

Mechanism

NIH ODS includes oral bisphosphonates among the drugs magnesium interacts with, for the same reason as calcium: binding in the stomach and loss of the small absorbed fraction. Magnesium antacids fall under the label's warning together with other oral medicines.

Symptoms

No direct symptoms. It surfaces as a lack of densitometric response.

Management

Respect the same 30-minute window after alendronate. Evening magnesium does not interfere with the morning bisphosphonate dose.

Sources

Pair details →Magnesium (oral salts: citrate, glycinate, oxide, sulfate) →

Label mentions2 mentions

Verbatim lines from the interaction sections, in the language of the label

From this drug’s label

ModerateAINEclass named in the label
«Debido a que el uso de AINEs se asocia con irritación gastrointestinal, se recomienda precaución durante el uso concomitante con alendronato.»
AEMPS, section 4.5 · Open on CIMA
antiácidosclass named in the label
«Es probable que, si se toman al mismo tiempo, alimentos y bebidas (incluida el agua mineral), los suplementos de calcio, los antiácidos y otros medicamentos orales interfieran la absorción de…»
AEMPS, section 4.5 · Open on CIMA

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Frequently asked

What is Alendronic acid used for?

Alendronic acid is evaluated for the following indications with varying evidence strength: Postmenopausal osteoporosis (evidence tier A), Glucocorticoid-induced osteoporosis (evidence tier A), Paget's disease of bone (evidence tier B). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Alendronic acid?

Common side effects of Alendronic acid (≥ 1 in 100): Abdominal pain, reflux, esophagitis, Muscle, bone, and joint pain, Headache, Mild hypocalcemia. See the Safety section for uncommon and serious reactions.

Is Alendronic acid safe during pregnancy?

Bisphosphonates accumulate in the skeleton for years. Contraindicated in pregnancy. Reliable contraception is required if therapy is needed in women of reproductive age.

Is Alendronic acid compatible with breastfeeding?

No data on milk excretion. Not used during lactation.

Who should not take Alendronic acid?

Alendronic acid is contraindicated in: Bisphosphonate hypersensitivity; Hypocalcemia; Esophageal abnormalities (achalasia, stricture) or inability to stay upright for 30 minutes; Severe renal impairment (eGFR under 35); Pregnancy and lactation. Full list in the Safety section.

Official sources

Direct links to regulator labels. Open in a new tab.

AEMPS / CIMALabel dated 10/02/2024

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