Short answer: In the label's 3-year trial of 7,736 postmenopausal women, Reclast side effects that ran above placebo included fever (17.9% vs 4.6%), headache (12.4% vs 8.1%), muscle pain (11.7% vs 3.7%), flu-like illness (8.8% vs 2.7%) and chills (5.4% vs 1.0%). Most started within 3 days of the infusion. The warnings cover kidney problems, low calcium, jaw problems and unusual thigh fractures. There is no boxed warning.
What Reclast is approved for: Reclast is a bisphosphonate approved to treat and prevent osteoporosis in postmenopausal women, to increase bone mass in men with osteoporosis, to treat and prevent steroid (glucocorticoid)-induced osteoporosis in people taking 7.5 mg or more of prednisone a day for at least 12 months, and to treat Paget's disease of bone (sections 1.1 to 1.5). The label says the best length of use has not been set, and people at low fracture risk may be considered for stopping after 3 to 5 years (section 1.6).
Source
RECLAST (zoledronic acid) injection, for intravenous use, prescribing information and Medication Guide. Sandoz. DailyMed, version published February 13, 2026. DailyMed setid 5a9b3737-9ce6-4a89-b76e-6aab79eba9cf
No. The current Reclast label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Reclast.
| Adverse reaction | Study 1 Reclast % (N = 3862) | Study 1 Placebo % (N = 3852) | Study 2 Reclast % (N = 1054) | Study 2 Placebo % (N = 1057) |
|---|---|---|---|---|
| Anemia | 4.4 | 3.6 | 5.3 | 5.2 |
| Dehydration | 0.6 | 0.6 | 2.5 | 2.3 |
| Anorexia | 2.0 | 1.1 | 1.0 | 1.0 |
| Headache | 12.4 | 8.1 | 3.9 | 2.5 |
| Dizziness | 7.6 | 6.7 | 2.0 | 4.0 |
| Vertigo | 4.3 | 4.0 | 1.3 | 1.7 |
| Atrial fibrillation | 2.4 | 1.9 | 2.8 | 2.6 |
| Hypertension | 12.7 | 12.4 | 6.8 | 5.4 |
| Nausea | 8.5 | 5.2 | 4.5 | 4.5 |
| Diarrhea | 6.0 | 5.6 | 5.2 | 4.7 |
| Vomiting | 4.6 | 3.2 | 3.4 | 3.4 |
| Abdominal pain upper | 4.6 | 3.1 | 0.9 | 1.5 |
| Dyspepsia | 4.3 | 4.0 | 1.7 | 1.6 |
| Arthralgia | 23.8 | 20.4 | 17.9 | 18.3 |
| Myalgia | 11.7 | 3.7 | 4.9 | 2.7 |
| Pain in extremity | 11.3 | 9.9 | 5.9 | 4.8 |
| Shoulder pain | 6.9 | 5.6 | 0.0 | 0.0 |
| Bone pain | 5.8 | 2.3 | 3.2 | 1.0 |
| Neck pain | 4.4 | 3.8 | 1.4 | 1.1 |
| Muscle spasms | 3.7 | 3.4 | 1.5 | 1.7 |
| Osteoarthritis | 9.1 | 9.7 | 5.7 | 4.5 |
| Musculoskeletal pain | 0.4 | 0.3 | 3.1 | 1.2 |
| Pyrexia | 17.9 | 4.6 | 8.7 | 3.1 |
| Influenza-like illness | 8.8 | 2.7 | 0.8 | 0.4 |
| Fatigue | 5.4 | 3.5 | 2.1 | 1.2 |
| Chills | 5.4 | 1.0 | 1.5 | 0.5 |
| Asthenia | 5.3 | 2.9 | 3.2 | 3.0 |
| Peripheral edema | 4.6 | 4.2 | 5.5 | 5.3 |
| Pain | 3.3 | 1.3 | 1.5 | 0.5 |
| Malaise | 2.0 | 1.0 | 1.1 | 0.5 |
| Hyperthermia | 0.3 | < 0.1 | 2.3 | 0.3 |
| Chest Pain | 1.3 | 1.1 | 2.4 | 1.8 |
| Creatinine renal clearance decreased | 2.0 | 2.4 | 2.1 | 1.7 |
Study 1: 3-year placebo-controlled trial of 7,736 postmenopausal women aged 65 to 89, one 5 mg infusion a year for three doses. Study 2: 2,127 men and women aged 50 to 95 with a recent low-trauma hip fracture, followed about 2 years. Reactions are listed if more frequent on Reclast in either trial. Deaths from any cause: 3.4% vs 2.9% in Study 1 and 9.6% vs 13.3% in Study 2.
| Adverse reaction | Reclast once per year % (n = 198) | Reclast once % (n = 181) | Placebo % (n = 202) |
|---|---|---|---|
| Headache | 14.6 | 20.4 | 11.4 |
| Nausea | 17.7 | 11.6 | 7.9 |
| Arthralgia | 27.3 | 18.8 | 19.3 |
| Myalgia | 19.2 | 22.7 | 6.9 |
| Back pain | 18.2 | 16.6 | 11.9 |
| Pain in extremity | 11.1 | 16.0 | 9.9 |
| Pain | 24.2 | 14.9 | 3.5 |
| Pyrexia | 21.7 | 21.0 | 4.5 |
| Chills | 18.2 | 18.2 | 3.0 |
| Fatigue | 14.6 | 9.9 | 4.0 |
2-year prevention trial of 581 postmenopausal women with low bone mass: Reclast at the start and at Month 12, Reclast once at the start, or placebo. Shown are the rows at 10% or more in any group; the full table has more. Stopping because of side effects: 7.1% and 7.2% on Reclast vs 3.0% on placebo.
Acute phase reaction in Study 1: fever (18%), muscle pain (9%), flu-like symptoms (8%), headache (7%) and joint pain (7%), mostly within the first 3 days after the infusion and usually gone within 3 days, though it could take up to 7 to 14 days. In Study 2, where acetaminophen was given, fever was 7% and joint pain 3%. The symptoms became less common with later doses.
Kidney: a temporary rise in serum creatinine within 10 days of dosing in 1.8% on Reclast vs 0.8% on placebo, which resolved without specific treatment.
Atrial fibrillation in Study 1: serious events in 1.3% (50 of 3862) vs 0.4% (17 of 3852) on placebo; all atrial fibrillation events 2.5% vs 1.9%. Over 90% occurred more than a month after the infusion. In Study 2, serious events were 1.0% vs 1.2%.
Calcium below 7.5 mg/dL after the infusion in about 0.2% of women in Study 1, with no symptomatic cases. In Paget's disease trials, about 21% had calcium below 8.4 mg/dL 9 to 11 days after the infusion.
Eye inflammation (iritis, uveitis, episcleritis) in 1 (less than 0.1%) to 9 (0.2%) people on Reclast vs 0 to 1 on placebo in the osteoporosis treatment trials, and 4 (1.1%) vs 0 in the prevention trial. Infusion-site reactions: 0% to 0.7% vs 0% to 0.5%.
Men with osteoporosis vs a weekly oral bisphosphonate: muscle pain 19.6% vs 6.8%, fatigue 17.6% vs 6.1%, headache 15.0% vs 6.1%, pain 11.8% vs 4.1%, chills 9.8% vs 2.7%, flu-like illness 9.2% vs 2.0%.
Paget's disease vs risedronate over 6 months: acute phase reaction symptoms in 25% vs 8%; headache 11% vs 10%, flu-like illness 11% vs 6%, fever 9% vs 2%, rigors 8% vs 1%, low calcium 3% vs 1%.
Reported after approval: acute kidney failure needing hospital care or dialysis, or fatal, rarely; allergic reactions including anaphylaxis, hives, angioedema, Stevens-Johnson syndrome and bronchoconstriction; asthma flare-ups; low calcium and low phosphate; jaw and other bone osteonecrosis; atypical fractures; eye inflammation; and low blood pressure in people with risk factors.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not use it. People with low blood calcium, creatinine clearance under 35 mL/min or signs of acute kidney impairment, and people with a known allergy to zoledronic acid or any part of Reclast.
Zometa contains the same drug. Reclast has the same active ingredient as Zometa, used for cancer. People being treated with Zometa should not be given Reclast.
Low blood calcium. Existing low calcium and mineral problems are treated before starting. Low calcium after Reclast is a significant risk in Paget's disease, and everyone is taught the symptoms and the importance of calcium and vitamin D.
Kidney problems. A single dose is never more than 5 mg and the infusion lasts at least 15 minutes. Acute kidney failure has occurred, even after one dose, with rare hospital stays, dialysis or deaths, mostly with existing kidney problems, older age, diuretics, kidney-harming medicines or dehydration. Creatinine clearance is calculated before each dose, and people are well hydrated first.
Osteonecrosis of the jaw. Jaw bone death has been reported with bisphosphonates, mostly in cancer patients having dental work. The prescriber does a routine oral exam before starting, and a dental exam is considered for people with risk factors. Risk may grow with longer exposure.
Unusual thigh bone fractures. Atypical low-trauma fractures of the thigh bone and other bones have been reported, often after weeks to months of dull, aching thigh pain. Anyone with thigh or groin pain is checked for a fracture, and a break in treatment is considered.
Severe bone, joint and muscle pain. Severe, sometimes incapacitating pain has been reported, from one day to several months after starting. Future doses may be withheld if severe symptoms develop. Most people got better after stopping.
Asthma and aspirin sensitivity. Bronchoconstriction has been reported in aspirin-sensitive people on bisphosphonates, so Reclast is used with caution in them.
From the Medication Guide that comes with Reclast:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.