Aromatase Inhibitors: An Overview

Aromatase inhibitors are a class of medicines that reduce the body's production of estrogen. This page explains, in neutral terms, what they are, who they may be considered for after diagnosis, how they generally work, the common forms, how they are monitored, and the considerations to discuss with a clinician.

What aromatase inhibitors are

Estrogen is a hormone made in several parts of the body. An enzyme called aromatase converts certain hormones into estrogen, and in some tissues this is an important source of the estrogen circulating in the body. Aromatase inhibitors are medicines that block this enzyme, which lowers how much estrogen is produced. By acting on the production step, they reduce overall estrogen activity rather than directly removing hormone that is already present.

This mechanism is most relevant where the body's estrogen comes largely from aromatase activity in tissues outside the ovaries, which is one reason a person's menopausal status matters to how these medicines are used. A clinician considers where a person's estrogen is mainly coming from when judging whether this class fits the situation.

Who they may be considered for

Aromatase inhibitors are generally considered after a clinician has made a diagnosis and reviewed a person's full clinical picture. They are most familiar in the care of certain hormone-sensitive breast cancers, where lowering estrogen is part of a treatment plan; that use is directed within specialist cancer care. They are also discussed in some other clinical situations, including certain hormonal and fertility-related contexts, where a clinician judges them appropriate.

Because the effect of these medicines depends on how the body makes estrogen, their suitability differs by individual circumstances, such as menopausal status and the specific condition being treated. They are one of several options a clinician may discuss, and the most appropriate choice is decided together. The table below illustrates, in general terms, how this class differs from another hormone-related approach sometimes discussed for estrogen-sensitive conditions.

This comparison is illustrative; which approach fits a given person is decided within specialist care.

How they generally work

By blocking the aromatase enzyme, these medicines generally reduce the conversion of other hormones into estrogen, which lowers estrogen levels in the body. In the context of hormone-sensitive conditions, the aim is to limit estrogen's effect on tissue that responds to it. The effect builds over time as estrogen levels decline, rather than acting suddenly. How fully estrogen is lowered, and what that means clinically, depends on the individual and the setting in which the medicine is used.

Because estrogen has roles throughout the body, lowering it can have effects beyond the tissue a treatment is aimed at, which is part of why monitoring and follow-up are built into care with these medicines.

It can help to picture two different ways of reducing a hormone's effect. One way lowers how much of the hormone the body makes, which is the approach aromatase inhibitors take. Another way leaves production largely as it is but blocks the hormone from acting at its receptor. Both can reduce estrogen-driven activity, but they differ in their effects on measured estrogen levels and in the considerations that come with them. Understanding which strategy a treatment uses helps explain why monitoring and possible side effects differ between approaches, and why a specialist chooses among them for a given situation.

Common forms and routes

Described generally, aromatase inhibitors are usually taken by mouth as a tablet, often on a daily schedule. Several agents exist within the class, and a clinician selects among them based on the clinical situation. The duration of treatment varies widely depending on the condition and the goals of care. This page does not give doses or schedules, which are individualized.

How clinicians typically monitor it

Monitoring combines how a person feels with relevant tests and reviews. Clinicians commonly:

• Review symptoms and how the person is tolerating treatment over time.
• Consider bone health, since lowering estrogen can affect bone density, and may arrange bone-related assessment in some situations.
• Order condition-specific tests and follow-up appropriate to the reason for treatment.
• Reassess periodically to confirm the approach still fits the person's goals and health status.

Considerations and risks

As with any medicine, aromatase inhibitors can have side effects. Because they lower estrogen, commonly reported effects can include joint or muscle aches, hot flushes, and tiredness. Over time, reduced estrogen can affect bone density, which is one reason a clinician may pay attention to bone health and discuss ways to support it.

There are situations in which these medicines are not appropriate, including during pregnancy, and a clinician reviews individual circumstances before starting. People are usually advised to report new or troubling symptoms so that care can be adjusted. Because some uses outside cancer care, such as certain fertility-related contexts, are areas where practice and evidence continue to develop, a clinician frames those uses carefully. These points are why ongoing clinical oversight matters rather than adjusting treatment informally.

Shared decision-making

Choosing whether to use an aromatase inhibitor is a collaborative process guided by your diagnosis, results, and preferences. It can help to discuss possible benefits, possible side effects such as effects on bones and joints, how long treatment may last, and alternatives. Explore related material in our conditions and hormones sections, learn about testing under blood tests, and see other options in the treatments overview.