What the label lists and what reports show
Anastrozole side effects
Anastrozole's FDA label: “In the ATAC trial, the most common reported adverse reaction (>0.1%) leading to discontinuation of therapy for both treatment groups was hot flashes, although there were fewer patients who discontinued therapy as a result of hot flashes in the ARIMIDEX group.” FAERS holds 36,521 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is fatigue (3,445 reports).
- Generic listed
Check it at the source: the anastrozole FDA label on DailyMed (effective March 2, 2026, ANI Pharmaceuticals, Inc.); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of ARIMIDEX?ARIMIDEX may cause serious side effects including: • See “ What is the most important information I should know about ARIMIDEX ?” • bone thinning or weakness (osteoporosis). ARIMIDEX lowers estrogen in your body, which may cause your bones to become thinner and weaker. This may increase your risk of fractures, especially of your spine, hip and wrist. Your healthcare provider may order a bone mineral density test before you start and during treatment with ARIMIDEX to check you for bone changes. • increased blood cholesterol (fat in the blood). Your healthcare provider may do blood tests to check your cholesterol while you are taking ARIMIDEX. • skin reactions. Stop taking ARIMIDEX and call your healthcare provider right away if you get any skin lesions, ulcers, or blisters. • severe allergic reactions. […]
Source: FDA drug label, NDA020541 (Ani Pharms), as published by ANI Pharmaceuticals, Inc., effective March 2, 2026 (SPL set acbfaaa9-503c-4691-9828-76a7146ed6de), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsIn the ATAC trial, the most common reported adverse reaction (>0.1%) leading to discontinuation of therapy for both treatment groups was hot flashes, although there were fewer patients who discontinued therapy as a result of hot flashes in the ARIMIDEX group.
Table 3 - Adverse Reactions Occurring with an Incidence of at Least 5% in Trials 0030 and 0027
| Reaction | Body system Adverse Reaction A patient may have had more than 1 adverse event. ARIMIDEX (N=506) | Number (%) of subjects Tamoxifen (N=511) |
|---|---|---|
| Asthenia | 83 (16) | 81 (16) |
| Pain | 70 (14) | 73 (14) |
| Back pain | 60 (12) | 68 (13) |
| Headache | 47 (9) | 40 (8) |
| Abdominal pain | 40 (8) | 38 (7) |
| Chest pain | 37 (7) | 37 (7) |
| Flu syndrome | 35 (7) | 30 (6) |
| Pelvic pain | 23 (5) | 30 (6) |
| Vasodilation | 128 (25) | 106 (21) |
| Hypertension | 25 (5) | 36 (7) |
| Nausea | 94 (19) | 106 (21) |
| Constipation | 47 (9) | 66 (13) |
| Diarrhea | 40 (8) | 33 (6) |
| Vomiting | 38 (8) | 36 (7) |
| Anorexia | 26 (5) | 46 (9) |
| Peripheral edema | 51 (10) | 41 (8) |
| Bone pain | 54 (11) | 52 (10) |
| Dizziness | 30 (6) | 22 (4) |
| Insomnia | 30 (6) | 38 (7) |
| Depression | 23 (5) | 32 (6) |
| Hypertonia | 16 (3) | 26 (5) |
| Cough increased | 55 (11) | 52 (10) |
| Dyspnea | 51 (10) | 47 (9) |
| Pharyngitis | 49 (10) | 68 (13) |
| Rash | 38 (8) | 34 (8) |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedSerious adverse reactions with ARIMIDEX occurring in less than 1 in 10,000 patients, are: 1) skin reactions such as lesions, ulcers, or blisters; 2) allergic reactions with swelling of the face, lips, tongue, and/or throat. This may cause difficulty in swallowing and/or breathing; and 3) changes in blood tests of the liver function, including inflammation of the liver with symptoms that may include a general feeling of not being well, with or without jaundice, liver pain or liver swelling [see Adverse Reactions ( 6.2 )]. Common adverse reactions (occurring with an incidence of ≥10%) in women taking ARIMIDEX included: hot flashes, asthenia, arthritis, pain, arthralgia, hypertension, depression, nausea and vomiting, rash, osteoporosis, fractures, back pain, insomnia, headache, bone pain, peripheral edema, increased cough, dyspnea, pharyngitis and lymphedema. In the ATAC trial, the most common reported adverse reaction (>0.1%) leading to discontinuation of therapy for both treatment groups was hot flashes, although there were fewer patients who discontinued therapy as a result of hot flashes in the ARIMIDEX group. Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
Source: FDA drug label, NDA020541 (Ani Pharms), as published by ANI Pharmaceuticals, Inc., effective March 2, 2026 (SPL set acbfaaa9-503c-4691-9828-76a7146ed6de), via openFDA; the full label on DailyMed
What do FAERS reports show?
36,521 reports list anastrozole among the medicines taken, each a report of something that happened, not proof the medicine caused it; 2,430 are coded as a death and 7,951 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 22 reactions below, 16 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Anastrozole: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions