Alendronic Acid (Alendronate): Side Effects and What to Expect

What is alendronic acid, and how does it work?

Alendronic acid is a type of medicine called a bisphosphonate, used to treat and prevent osteoporosis — the condition in which bones become weaker and more likely to break. The NHS explains that it "slows the rate that bone is broken down in your body," which helps maintain bone density and reduces your risk of a broken bone NHS. It is prescribed for people who "already have osteoporosis, or are at risk of developing it," including those on long-term steroids NHS.

Your skeleton renews itself constantly, with cells that build bone and cells that break it down. In osteoporosis, breakdown outpaces building. Alendronic acid works on that balance rather than on the causes behind it — so understanding what causes osteoporosis in the first place still matters. The benefit builds gradually over months, not days, which is one reason people are asked to keep taking it consistently.

How do you take alendronic acid correctly?

This is the single most important practical question — take it first thing in the morning, on an empty stomach, swallowed whole with a full glass of plain tap water, and then stay upright for at least 30 minutes before you eat, drink or take anything else. The usual dose is a 70mg tablet once a week, though a 10mg daily version exists NHS.

The NHS instructions are specific:

• Swallow the tablet whole — with a full glass of plain tap water, not just a sip. Do not chew, crush or suck it, which can cause mouth or food-pipe ulcers.
• On an empty stomach — before you have anything to eat or drink other than plain tap water, and before any other medicines you swallow.
• With tap water only — not mineral water (still or sparkling), tea, coffee, juice or milk, which reduce how well it is absorbed.
• Sitting up or standing — and stay upright for 30 minutes afterwards.
• Not at bedtime — take it at the same time each day or week.

After 30 minutes you can eat and drink normally NHS. Staying upright is not a detail to skip — it helps stop the tablet lingering in and irritating your food pipe, where the NHS notes alendronic acid can cause ulcers NHS.

What are the common side effects of alendronic acid?

The most common side effects are digestive — indigestion, bloating or wind, constipation or diarrhoea — which the NHS lists as affecting more than 1 in 100 people. Others in that group include dizziness, headaches, muscle or joint pain, swollen joints or legs, tiredness and hair loss NHS.

Most are mild and often settle with time. Taking the tablet exactly as directed — whole, upright, with a full glass of water, on an empty stomach — is the main thing that keeps the tummy and food-pipe effects to a minimum. If a side effect is troubling you or won't go away, your GP or pharmacist can help rather than you simply stopping.

What are the rare but serious side effects?

Alendronic acid can occasionally cause more serious problems — irritation or ulcers of the food pipe, osteonecrosis of the jaw, and unusual thigh-bone fractures — but it is important to keep these in proportion: they are uncommon, and for most people the fracture-prevention benefit outweighs them.

• The food pipe (oesophagus). This is the one the upright rule protects against. The NHS advises you to stop taking alendronic acid and call 111 if you get heartburn, heartburn that gets worse, or problems or pain when swallowing, as these can signal ulcers in the food pipe NHS.
• The jaw (osteonecrosis of the jaw, or ONJ). A condition where healing inside the mouth is delayed, usually after dental work. The Royal Osteoporosis Society estimates that between 1 and 10 people in every 10,000 taking osteoporosis drug treatments will develop ONJ Royal Osteoporosis Society.
• The thigh bone (atypical femoral fracture). The Royal Osteoporosis Society puts this in context: if 1,000 people were taking treatments linked to these fractures, fewer than 1 would have one. They are linked with taking treatment for many years, and the main warning sign is new, unexplained pain in the thigh or groin — which should prompt a doctor's appointment Royal Osteoporosis Society.

The NHS frames the long-term picture honestly: "In a very small number of people, taking alendronic acid for more than 2 years can increase their chances of getting a rare type of bone damage in their inner ear and certain types of breaks to their thigh bones" — while noting that, overall, the benefits generally outweigh the risks NHS.

What should you tell your dentist before dental treatment?

Tell your dentist you take alendronic acid, and keep your teeth and gums healthy — good oral hygiene and regular check-ups are the main way to keep the already-small risk of jaw problems small. The NHS notes that jawbone damage is a rare side effect "which your dentist can check for" NHS, and the Royal Osteoporosis Society says all dentists should be aware of how to manage patients on osteoporosis drug treatments Royal Osteoporosis Society.

Reassuringly, the Society also says that if your teeth and gums are healthy you are unlikely to need a special check-up before treatment, and — importantly — that stopping or pausing your osteoporosis medicine is unlikely to reduce your risk of ONJ Royal Osteoporosis Society. In other words, don't stop your tablets before a filling or extraction without asking your GP or dentist first.

Can you take collagen, calcium or other supplements with alendronic acid?

Not at the same time. The NHS rule is that alendronic acid must be taken with nothing but plain tap water, before any other food, drink or medicines you swallow, with a 30-minute gap afterwards NHS. A collagen drink or powder counts as food or drink, and a calcium or vitamin D tablet counts as another medicine you swallow — so take any of these later in the day, well separated from your weekly tablet, rather than alongside it.

This is a timing point, not a reason to give up on either. Calcium, vitamin D and protein all matter for bone, and if you are curious about supplements our guide to collagen and bone health looks at the evidence. For the specifics of which supplement to take and exactly when, your pharmacist is the right person to ask.

How long will you take alendronic acid, and what is a drug holiday?

Most people take alendronic acid for at least 3 to 5 years, after which your doctor reviews the benefits and risks and decides whether you should continue — and some are then advised to pause, which is sometimes called a "drug holiday." That review point is set out by the NHS NHS, and the Royal Osteoporosis Society notes that after about five years on a bisphosphonate you may be advised to pause treatment Royal Osteoporosis Society.

A pause is not the same as failure or giving up — it is a deliberate way to balance ongoing fracture protection against the small risks that rise with very long use. Whether a break is right for you depends on your own fracture risk, which is often estimated with a tool like FRAX; our guide to fracture risk and FRAX explains how that works. It is a decision for you and your clinician, not one to make alone.

How do you know if alendronic acid is working?

You cannot feel your bones getting stronger, so the only way to know whether treatment is holding your bone density is to measure it — which is where repeat bone scans come in. A bone density scan measures density, which the Royal Osteoporosis Society describes as one factor in overall bone strength, considered alongside things like age and family history — and scans are normally repeated every two to five years to monitor bone strength Royal Osteoporosis Society.

That monitoring role is where a radiation-free approach fits. Because a drug-holiday decision hinges on where your bone density actually stands, being able to track it over a course of treatment is genuinely useful. Standard DEXA uses a small X-ray dose; REMS (Radiofrequency Echographic Multi Spectrometry) is radiation-free, so it can be repeated safely to follow change over time. It complements — rather than replaces — your GP's plan and any decision about staying on, pausing or changing treatment. If you are wondering how much can be regained, our guide to whether osteoporosis can be reversed is a useful read. You can also book a radiation-free bone health assessment or learn more about our bone health assessment.

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This article is for general information and is not a substitute for advice from your GP, pharmacist or specialist — never start, stop or change a prescribed medicine on your own. It is part of our bone health series; to understand the bigger picture, see what causes osteoporosis.