The half-life of an anti-estrogen drug refers to the time it takes for half of the drug's active substance to be eliminated from the body. Anti-estrogen drugs are commonly used in various medical contexts, including the treatment of hormone-receptor-positive breast cancer and, in some cases, by bodybuilders or athletes to counteract the estrogenic side effects of anabolic steroids. There are several types of anti-estrogen drugs, each with its own specific half-life:

1. **Selective Estrogen Receptor Modulators (SERMs)** such as Tamoxifen and Raloxifene:
- **Tamoxifen**: The half-life is about 5 to 7 days, but its active metabolite, endoxifen, has a longer half-life of about 14 days.
- **Raloxifene**: Has a half-life of approximately 27.7 hours.

2. **Aromatase Inhibitors (AIs)**, which include Anastrozole (Arimidex), Letrozole (Femara), and Exemestane (Aromasin):
- **Anastrozole**: The half-life is approximately 46.8 hours.
- **Letrozole**: The half-life is about 2 days (48 hours).
- **Exemestane**: The half-life is approximately 24 hours, but it irreversibly inhibits the aromatase enzyme, making its duration of effect longer than the half-life suggests.

3. **Estrogen Receptor Downregulators (ERDs)** like Fulvestrant:
- **Fulvestrant**: Has a significantly longer half-life, with initial half-life estimates around 40 hours, but due to its depot injection formulation, it has a terminal half-life of about 28 to 40 days.

The half-life of these drugs can influence their dosing schedule. For example, drugs with a shorter half-life may need to be taken more frequently than those with a longer half-life. The choice of anti-estrogen medication and its dosing regimen depends on several factors, including the condition being treated, the specific drug's pharmacokinetics, and the patient's overall health status.

It's important to use these medications under the guidance of a healthcare professional to ensure their safe and effective use, especially considering their potential side effects and interactions with other medications.