Health Guides
Anastrozole vs Letrozole: Comparing Two Aromatase Inhibitors
Anastrozole vs letrozole explained: how these aromatase inhibitors work, usual doses, side effects, tamoxifen as an alternative, and buying generics with a prescription.
- Quality generic medicines
- Prescription required
- Ships to the USA, UK, Canada & Europe
Anastrozole vs letrozole is one of the most common comparisons people look up after an oncologist recommends hormone therapy for breast cancer. Both are aromatase inhibitors, both are taken as a single tablet once a day, and both are used for hormone receptor-positive breast cancer in women after the menopause. Anastrozole is the generic version of Arimidex, and letrozole is the generic version of Femara.
This guide explains how the two medicines work, their usual doses, how they compare on effectiveness and side effects, where tamoxifen fits in, and what to check if you plan to buy generic Arimidex or Femara online with your prescription. It is written for patients and carers and does not replace the advice of your oncologist, the right person to decide which medicine suits you.
Key takeaways
- Anastrozole and letrozole are both aromatase inhibitors that lower oestrogen (estrogen) levels in women after the menopause.
- The usual dose is anastrozole 1 mg once daily or letrozole 2.5 mg once daily, as set by your oncologist.
- In the anastrozole vs letrozole comparison, both are considered effective, and side effects such as joint aches, hot flushes and bone thinning are similar.
- They are not used on their own in women before the menopause, and they should not be taken together with tamoxifen or oestrogen-containing products.
- A valid prescription is required for every order, and any switch between medicines or brands should be agreed with your oncologist.
What are anastrozole and letrozole?
Anastrozole and letrozole belong to a group of medicines called aromatase inhibitors. A third, exemestane, works slightly differently. All are hormone (endocrine) therapies rather than chemotherapy.
Many breast cancers are hormone receptor-positive. This means the cancer cells have receptors for oestrogen and, in some cases, progesterone, and oestrogen can encourage them to grow. Lowering the amount of oestrogen in the body can slow or stop the growth of these cancers, or lower the chance of the cancer coming back after treatment.
Both medicines are available as low-cost generics. You can see the generic versions stocked at RxPillTab in our oncology medicines range, including Armotraz 1 (anastrozole 1 mg) and Letzol-Sure 2.5 (letrozole 2.5 mg).
How aromatase inhibitors work
After the menopause, the ovaries stop producing most of the body’s oestrogen. A smaller amount is still made in other tissues, such as fat, muscle and the adrenal glands, by an enzyme called aromatase. Aromatase converts other hormones (androgens) into oestrogen.
Anastrozole and letrozole block aromatase. This sharply reduces the amount of oestrogen in the body of a post-menopausal woman, so hormone-sensitive cancer cells receive much less of the signal that drives their growth. They do not block the oestrogen receptor itself; that is how tamoxifen works, which is covered further down.
Why they are not used alone before the menopause
Before the menopause, the ovaries are still the main source of oestrogen. An aromatase inhibitor on its own cannot lower these levels enough, and the drop in oestrogen can even prompt the ovaries to work harder. For this reason, anastrozole and letrozole are not used alone in pre-menopausal women. Some pre-menopausal women are given an aromatase inhibitor together with treatment that switches off the ovaries (ovarian suppression), but this is a specialist decision made by the oncologist.
Usual doses of anastrozole and letrozole
Both are taken by mouth once a day, with or without food, at about the same time each day.
- Anastrozole: 1 mg once daily.
- Letrozole: 2.5 mg once daily.
These are the licensed doses, and higher doses are not used to get a stronger effect. If you miss a dose, take it when you remember unless it is nearly time for the next one; do not take two doses together. The patient leaflet that comes with your medicine gives full instructions.
Treatment usually lasts several years. Five years is common in the adjuvant setting, and some women are advised to continue for longer, sometimes after a period on tamoxifen. Only your oncologist can decide how long you should take it.
Adjuvant vs advanced breast cancer: how they are used
In general terms, there are two main situations in which these medicines are prescribed:
- Adjuvant treatment (early breast cancer): taken after surgery, and sometimes after chemotherapy or radiotherapy, to lower the risk of the cancer returning. Some women take an aromatase inhibitor from the start; others switch to one after two to three years of tamoxifen. Letrozole is also used as extended therapy after five years of tamoxifen in some women.
- Advanced or metastatic breast cancer: used to slow the growth of cancer that has spread, either alone or alongside newer targeted medicines that the oncologist may add.
Anastrozole vs letrozole: how do they compare?
The short answer is that the two medicines are more alike than different. Both are non-steroidal aromatase inhibitors, both are taken once a day, and both lower oestrogen levels very effectively. Letrozole lowers oestrogen slightly more in laboratory measurements, but a large head-to-head study in early breast cancer did not find a meaningful difference in how well the two medicines prevented the cancer from returning or in survival.
| Feature | Anastrozole | Letrozole |
|---|---|---|
| Original brand | Arimidex | Femara |
| Medicine group | Non-steroidal aromatase inhibitor | Non-steroidal aromatase inhibitor |
| Usual dose | 1 mg once daily | 2.5 mg once daily |
| Main use | Hormone receptor-positive breast cancer after the menopause | Hormone receptor-positive breast cancer after the menopause |
| Effectiveness | Effective in early and advanced disease | Effective in early and advanced disease |
| Common side effects | Joint aches, hot flushes, tiredness, bone thinning | Joint aches, hot flushes, tiredness, bone thinning |
| Bone monitoring | Bone density scans usually advised | Bone density scans usually advised |
| Generic at RxPillTab | Armotraz 1 | Letzol-Sure 2.5 |
Because the results are so similar, the choice between anastrozole and letrozole is usually down to your oncologist’s experience, your other medical conditions, and how you tolerate the tablets.
Side effects of anastrozole vs letrozole
Side effect profiles are similar for both medicines, because the side effects come mainly from the drop in oestrogen. Not everyone gets them, and many settle after the first few months.
Common side effects
- Joint and muscle aches or stiffness, often worse in the morning
- Hot flushes and sweating
- Tiredness and low energy
- Vaginal dryness and lower interest in sex
- Headache, nausea, mood changes or trouble sleeping
Bone thinning and bone density monitoring
Lower oestrogen levels can cause bones to lose density over time, which raises the risk of osteoporosis and fractures. Your oncologist will usually arrange a bone density scan before or soon after you start, and repeat scans during treatment. You may be advised to take calcium and vitamin D, to stay active with weight-bearing exercise, and in some cases to take a bone-strengthening medicine.
When to get medical advice
Contact your doctor promptly if you notice severe or persistent joint pain, a new bone fracture, numbness or tingling in the hands, signs of an allergic reaction, yellowing of the skin or eyes, or any symptom that worries you.
Tamoxifen: the alternative hormone therapy
Tamoxifen is the other main hormone therapy for hormone receptor-positive breast cancer. Rather than lowering oestrogen levels, it blocks oestrogen from acting on the cancer cells. Unlike aromatase inhibitors, tamoxifen can be used both before and after the menopause, and it is also used in men with breast cancer.
Some women take tamoxifen first and then switch to anastrozole or letrozole, or the other way round. Tamoxifen has a different side effect profile, with a small increased risk of blood clots and changes in the lining of the womb, but generally less effect on the bones. You can read more in our guide on how to buy generic tamoxifen online.
Interactions and safety precautions
Tell your oncologist and pharmacist about every medicine, supplement and herbal product you take. Key points for both aromatase inhibitors:
- Do not take with tamoxifen. Taking an aromatase inhibitor at the same time as tamoxifen does not add benefit and may reduce the effect. They are used one after the other, not together.
- Avoid oestrogen-containing products. Hormone replacement therapy (HRT), some vaginal oestrogen products and oestrogen-containing contraceptives can work against the treatment. Ask your oncologist before using any of them.
- Pregnancy and breastfeeding: these medicines must not be used during pregnancy or breastfeeding.
Switching between brands or medicines
Generic anastrozole and letrozole contain the same active ingredient at the same strength as the original brands. Even so, agree any change of medicine, strength or brand with your oncologist. Do not switch between anastrozole and letrozole on your own, and do not stop treatment early without advice, even if you feel well.
Anastrozole price and letrozole price
Generic versions of Arimidex and Femara usually cost much less than the original brands, which matters for a treatment that may run for five years or more. The current anastrozole price and letrozole price for each pack size are shown on the product pages. When you compare prices, check that you are comparing the same strength (anastrozole 1 mg or letrozole 2.5 mg) and the same number of tablets.
How to buy generic anastrozole and letrozole online safely
If you buy medicine online, especially a long-term cancer treatment, follow these steps:
- Have a valid prescription. A valid prescription is required for every order of a prescription medicine, including anastrozole and letrozole.
- Check the medicine and strength. Make sure the product matches your prescription exactly: anastrozole 1 mg (generic Arimidex) or letrozole 2.5 mg (generic Femara).
- Check the pack size. Order enough tablets to cover the time until your next supply, allowing for delivery time, so you do not run out.
- Plan for delivery. Orders are shipped worldwide by EMS or registered mail in discreet packaging, delivered to the US, UK, Europe and Canada. Our how to order page explains the steps.
- Tell your doctor. Let your oncologist know which generic brand you are taking so it is recorded in your notes.
For more general advice on choosing a safe online supplier, see our guide on how to buy generic medicines online safely.
Frequently asked questions
Anastrozole vs letrozole: which is better?
Neither has been shown to be clearly better overall. Both are effective aromatase inhibitors for hormone receptor-positive breast cancer after the menopause, with similar side effects. Your oncologist will choose the one that best suits your situation.
Can I switch from anastrozole to letrozole if I get side effects?
Some women do switch because they tolerate one medicine better than the other. However, this should only be done on the advice of your oncologist, as there may also be other ways to manage side effects.
Is generic Arimidex the same as the brand?
Generic Arimidex contains anastrozole 1 mg, the same active ingredient and strength as the original brand. The inactive ingredients, tablet shape and packaging may differ.
Can pre-menopausal women take letrozole 2.5 mg?
Not on its own for breast cancer. Aromatase inhibitors are only used in pre-menopausal women alongside treatment that suppresses the ovaries, and this is a decision for the oncologist.
Can I take anastrozole or letrozole with tamoxifen?
No. They are not taken together. Some women take tamoxifen first and then switch, or the other way round, as planned by their oncologist.
Do I need a prescription to order anastrozole or letrozole?
Yes. A valid prescription is required for every order of a prescription medicine, including both of these hormone therapies.
The information on this page is for general guidance only and does not replace professional advice. Always consult your doctor or pharmacist before starting any medicine. Read our full medical disclaimer.
Medicines mentioned in this guide
All medicines are supplied only against a valid prescription. Prices shown are for the smallest pack.
About this guide
Written by the rxptteam8. We base our guides on official sources such as the NHS, the US FDA, the EMA and MedlinePlus, and we update them when guidance changes. Last updated .