Eligard is a prescription injection used to treat advanced prostate cancer. It works by dramatically lowering testosterone levels in the body, since testosterone fuels the growth of most prostate cancer cells. The medication is given as a shot under the skin at intervals ranging from once a month to once every six months, depending on the dose.
How Eligard Treats Prostate Cancer
Prostate cancer cells typically rely on testosterone to grow and spread. Eligard belongs to a class of drugs called GnRH agonists, which shut down the body’s testosterone production through a somewhat counterintuitive process. Your brain naturally releases a hormone called GnRH in small pulses to signal the testes to produce testosterone. Eligard floods the system with a synthetic version of that signal continuously, which overwhelms the receptors and eventually causes them to stop responding. The result is that testosterone drops to extremely low levels, often called “castrate levels,” essentially starving the cancer of its primary fuel.
This suppression is highly effective. In clinical trials of the six-month formulation, 97% of patients reached castrate testosterone levels within 28 days of their first injection, with a median time of 21 days. In a smaller subset of 28 patients studied more closely, 100% achieved suppression by day 28. The effect is also reversible: testosterone production can resume after the medication is stopped.
Available Doses and Injection Schedule
Eligard comes in four strengths, each designed to last a specific period before the next injection is needed:
- 7.5 mg: one injection every month
- 22.5 mg: one injection every 3 months
- 30 mg: one injection every 4 months
- 45 mg: one injection every 6 months
All four are injected under the skin rather than into a muscle. The drug uses a special delivery system in which the active ingredient is mixed with a biodegradable polymer right before the injection. Once under the skin, this polymer forms a small solid deposit that slowly dissolves over weeks or months, releasing the medication at a steady rate. Your body eventually absorbs the polymer completely. Your doctor will choose a dose based on your treatment plan and how frequently you’re able to come in for appointments.
The Initial Testosterone Surge
One important detail about how Eligard works: before testosterone levels drop, they briefly rise. During the first one to two weeks of treatment, the drug initially stimulates testosterone production before the receptors become desensitized and shut down. This temporary surge, sometimes called a “flare,” can cause a short-term worsening of cancer-related symptoms like bone pain or urinary difficulty. Your doctor may prescribe a short course of another medication to block the effects of this flare during the first few weeks of treatment.
Common Side Effects
Because Eligard suppresses testosterone so thoroughly, many of its side effects mirror what you’d expect from very low hormone levels. In a clinical trial of 120 patients, the most frequently reported side effects were:
- Hot flashes: 57.5% of patients, the single most common effect
- Injection site reactions (burning, stinging, or pain): 54.2%
- Bruising at the injection site: 20%
- Fatigue: 18.3%
- Skin redness at the injection site: 15%
- Itching: 10.8%
- Dizziness: 8.3%
Hot flashes are by far the most noticeable side effect for most men and can range from mildly annoying to significantly disruptive. They tend to persist for as long as treatment continues. Injection site reactions are also common but typically resolve within a few days. Over longer periods of testosterone suppression, men may also experience reduced sex drive, erectile dysfunction, loss of muscle mass, increased body fat, mood changes, and decreased bone density. These effects generally develop gradually over months of treatment.
Uses Beyond Prostate Cancer
While Eligard is specifically approved for advanced prostate cancer, the active ingredient (leuprolide acetate) has a broader role in cancer treatment. Oncology guidelines recognize its use in certain cases of invasive breast cancer, ovarian cancer, fallopian tube cancer, and rare sex cord-stromal tumors. In these situations, the goal is similar: suppress the hormones that feed hormone-sensitive cancers. These uses are supported by national treatment guidelines, though they fall outside Eligard’s original FDA-approved indication.
What Treatment Looks Like Day to Day
For most men, Eligard treatment is straightforward. You visit your doctor’s office for an injection, then go home. The injection itself takes only a few minutes, and the most you’ll typically feel is a brief sting at the site. Depending on your dose, you won’t need another injection for one to six months. Between visits, your doctor will periodically check your testosterone levels and PSA (a protein that rises with prostate cancer activity) through simple blood tests to confirm the medication is working as expected.
Because the treatment suppresses testosterone for extended periods, it can affect bone health over time. Many men on long-term therapy are advised to take calcium and vitamin D supplements, stay physically active, and have periodic bone density checks. Weight-bearing exercise and resistance training can help counteract some of the muscle loss and bone thinning that come with low testosterone. The fatigue that many men experience often improves with regular physical activity as well, even when it feels counterintuitive to exercise while tired.