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Two leaders - Anastrozole and Letrozole. Which to choose better?

In this article, we are going to review two leaders among all modern preparations for cancer treatment. They are – Letrozole (the brand name of this preparation is Femara) and Anastrozole (the brand name of this preparation is Arimidex). Both these medications can be purchased as a brand preparations or as the generics and refer to the drugs which are widely used to treat breast cancer. The very important moment here is that both these preparations should be used only by women who have already gone through menopause. The mechanism of action of these medications is similar - they both are aimed at the inhibiting of aromatase. However, despite the similar way of action, side effects of these drugs vary and dosage for them is different. One more fact that is similar for both of these drugs is that they are prohibited to be used in combination with Tamoxifen as it can decrease their effect significantly.

What are anastrozole and letrozole? Let’s consider both of the reviewed preparations separately and try to sort out why they have become so popular and place the TOP positions among all other drugs with similar action nowadays.

We will start with Letrozole (or Femara). To understand the mechanism of this drug’s action let’s clarify one of the main reason for the breast cancer occurring. Specialists claim that among postmenopausal women the main reason for the breast cancer is the estrogen which circulates in the blood and cause the occurring of malignant tumors or their growth increasing. These estrogens are produced in the adrenal glands of the female organism. Letrozole, which is the oral drug, is aimed at the inhibiting of these estrogens production or rather inhibiting the enzyme which is responsible for their production. Because of such inhibition, this preparation refers to the “anti-estrogen” medications.

Speaking about Anastrozole, its mechanism of action is similar to the previously described one. This preparation is used for blocking the enzyme responsible for the enzymes production. Anastrozole is widely used as an auxiliary preparation for treating the malignant breast tumors. As a result – the delay in progression in the growth of the tumor and decrease of its size.

What are the side effects of anastrozole and letrozole?

What are anastrozole and letrozole

We have already mentioned that side effects of both these preparations differ. They have something similar and something absolutely different. Let’s check the most common side effects of each of these medications separately.

The possible negative effects of Letrozole taking are pain in the chest, digestive problems (diarrhea or constipation), headaches, tiredness, nausea or vomiting. Also, this preparation decreases the density of bones in your organism, so you should monitor your health condition regularly when taking this medication. Otherwise, you have a risk to get osteoporosis. In addition to this, Letrozole is not recommended for people with the high level of cholesterol in the organism as it may increase it to very high indexes, which may cause serious harm to your health.  

The most common negative effects of Anastrozole taking are skin rash, insomnia, decreased density of bones, pain in bones, nausea or vomiting, causeless depression, headaches, increased indexes of blood pressure, pain in different parts of the body, arthritis and hot flashes.

What is the dosage of anastrozole vs. letrozole? In order to maximally reduce the probability of side effects occurring you should be stick to the recommended dosage of the drug. For Letrozole, it is recommended to take 2.5 milligrams of the preparation per day regardless of food intake. You can take it either with or without food, it’s up to you. The recommended dosage of Anastrozole is 1 milligram (which is equal to one tablet) per day.

What drugs interact with anastrozole and letrozole?


Besides correct dosage on the general effectiveness of the drug and its side effects, other preparations may influence greatly. There are some medications which are prohibited from taking together with Letrozole or Anastrozole because they may not only significantly reduce the effectiveness of the drug but also cause a serious harm to your health. The main rule when taking both Letrozole and Anastrozole is not to take them together with Tamoxifen. This medication reduces the therapeutic effect of both Letrozole and Anastrozole. Also, we have mentioned that both these preparations are “anti-estrogen”, so taking them in combination with any other preparations which contain estrogen is highly undesirable as they may counteract each other.

Are anastrozole and letrozole safe to use while pregnant or breastfeeding? Both of the preparations reviewed in our article are completely prohibited from taking during pregnancy. They can cause serious harm to the fetal and terminate the pregnancy. Also, clinical studies don’t show the results of the influence of these preparations on the breast milk, so even taking them by the breastfeeding women is strictly prohibited in order not to cause irreparable damage to the health of the newborn child.


Summary. Summing up everything reviewed in this article we want to conclude that both of these preparations are effective for treatment of breast cancer and this is the main reason why they have become so popular nowadays. The main rule to get the desired therapeutic effect from them is to take the recommended dosage of these drugs, not to take them if you have some contraindications and not to exceed the duration of the therapeutic course. If you notice some side effects which were not listed above or any of side effects which don’t pass with the time, stop taking the preparation and consult your doctor as soon as its possible. Only in case of correct taking, these preparations will provide you with the desired therapeutic result.