Most Eligard side effects are mild to moderate and begin improving within a few months after your last injection, but some can linger for several months to over a year depending on how long you were on treatment. The timeline varies by side effect: injection site reactions clear up in days to weeks, while hormonal effects like hot flashes and fatigue take considerably longer because they’re tied to how quickly your testosterone levels recover.
Side Effects During Active Treatment
Eligard works by suppressing testosterone to very low levels, and that hormonal shift drives most of the side effects you’ll experience. In clinical trials, hot flashes were the most common, affecting about 74% of patients. Injection site reactions (pain, redness, itching, or discoloration) occurred in roughly 44%. Fatigue hit about 21% of patients, and dizziness about 14%. Other effects reported in at least 5% of patients included nausea, weight gain, muscle pain, reduced sex drive, erectile dysfunction, and urinary frequency.
The good news from the FDA’s medical review: out of 195 treatment-related side effects reported across 77 patients, only 4 were classified as severe. The vast majority were mild or moderate. That said, a small number of patients found the combined burden of side effects significant enough to stop treatment, typically around three to four months in, most often because of hot flashes, fatigue, decreased sex drive, or night sweats.
During the first week of treatment, you may actually notice a temporary flare of symptoms. Eligard causes a brief spike in testosterone before suppressing it, which can worsen prostate cancer symptoms for a short period. This flare is transient and typically resolves within one to two weeks.
Injection Site Reactions
Pain, redness, itching, and skin discoloration at the injection site are among the fastest side effects to resolve. These typically last a few days to a few weeks after each dose and don’t accumulate over time. Once you stop receiving injections, there’s no further trigger for these reactions, so they clear completely after your final dose heals.
How Long Hot Flashes Continue
Hot flashes are usually the most persistent and bothersome side effect, but they do resolve for nearly everyone. Research from the ASCENDE-RT trial found that hot flashes resolved a median of about 8 months after the last injection’s effects wore off. The timing closely tracked testosterone recovery: flashes tended to stop once testosterone climbed back to roughly mid-normal levels. By the end of follow-up, 99% of patients reported their hot flashes had fully resolved.
This means if your last Eligard injection was a 3-month formulation, you’d add roughly 3 months for the drug to clear your system, then another 7 to 8 months on average before hot flashes stop. So from your final injection date, expect roughly 10 to 12 months total before hot flashes are gone, though individual timelines vary.
Testosterone Recovery Sets the Clock
Most of Eligard’s side effects are downstream consequences of low testosterone, so the real question is how long it takes your body to start producing testosterone again. Research on patients discontinuing similar hormone-suppressing drugs found that about 55% of patients recovered to a normal testosterone level, with a median recovery time of roughly 4 months after the drug’s effects ended.
Several factors influence how quickly your testosterone bounces back. Older age, longer duration of treatment, and lower baseline testosterone before starting Eligard all tend to slow recovery. Men who were on Eligard for six months generally recover faster than those who received it for two or three years. Some men, particularly those who were older or on prolonged treatment, may not fully recover to their pre-treatment testosterone levels.
As testosterone rises, side effects peel away in a rough sequence. Injection site issues go first (days to weeks). Energy levels and mental clarity often start improving within a few months of your last dose. Hot flashes take longer, typically resolving around 8 months after the drug clears. Sexual function and muscle mass tend to be the slowest to return, sometimes taking several months to over a year.
Fatigue and Muscle Changes
Fatigue during Eligard treatment is common, and it doesn’t switch off the day your last injection wears off. According to Prostate Cancer UK, it can take several months to several years for energy levels to fully normalize after stopping hormone therapy. The same applies to muscle mass loss and weight gain that may have accumulated during treatment. Your body needs time to rebuild muscle tissue once testosterone is available again, and that process is gradual.
Exercise during and after treatment can meaningfully speed up recovery of both energy and muscle strength. Resistance training in particular helps counteract the muscle and bone density losses associated with low testosterone.
Effects That May Not Fully Reverse
While most side effects improve after stopping Eligard, some men find that certain changes don’t completely resolve. Bone density loss that occurred during treatment may not fully recover without intervention. Some degree of sexual dysfunction can persist, particularly in men who were on treatment for longer periods or who were older when they started. Breast tissue changes (gynecomastia) that developed during treatment sometimes remain.
The likelihood of permanent effects increases with longer treatment duration. Men who received Eligard for six months in combination with radiation therapy generally have a smoother recovery than those who were on it for two to three years. If your testosterone hasn’t shown meaningful recovery within 12 to 18 months after your last injection’s effects should have worn off, that delay is worth discussing with your treatment team, as additional evaluation or intervention may help.