Exemestane 25 mg, sold under the brand name Aromasin, causes side effects in most people who take it. The most common are hot flashes (affecting about 21% of patients), fatigue (16%), and increased sweating (12%). These tend to be most noticeable in the first few months and often improve over time. Beyond those, exemestane can affect your joints, bones, cholesterol, sleep, and mood in ways that are worth understanding before you start or while you’re adjusting to the medication.
Hot Flashes, Sweating, and Fatigue
Exemestane works by blocking the enzyme that produces estrogen in your body after menopause. That sharp drop in estrogen is what drives the most frequently reported side effects. Hot flashes tend to peak around three months into treatment and gradually ease after that. Fatigue affects roughly one in six patients and can range from mild tiredness to something that noticeably limits your daily energy. Increased sweating, especially night sweats, follows a similar pattern.
A quality-of-life study tracking patients over their first year on exemestane found that overall well-being dipped at the six-month mark but returned to baseline by twelve months. That trajectory is worth keeping in mind if you’re in the early weeks and feeling worse than expected.
Joint Pain and Stiffness
Joint symptoms are one of the more disruptive side effects of all aromatase inhibitors, including exemestane. In the major clinical trial for exemestane (the IES trial), about 12% of patients reported joint pain, though real-world studies suggest the number is higher. One study of 200 patients on aromatase inhibitors found that 47% reported joint symptoms, and roughly 20% of patients in another analysis stopped treatment entirely because the pain was too severe.
The pain typically shows up in the small joints of the hands and wrists, though it can affect knees, hips, and shoulders too. Imaging studies have shown increased fluid around the tendons and joint linings, which explains the stiffness many people feel, especially in the morning. The reassuring finding is that this type of joint pain does not cause structural damage to cartilage or bone the way arthritis does. It stems directly from estrogen depletion, not from joint deterioration.
Bone Density Loss and Fracture Risk
Estrogen plays a key role in maintaining bone strength, so blocking its production accelerates bone loss. In the Intergroup Exemestane Study, bone density at the spine dropped by 2.7% within the first six months of switching to exemestane. Hip density fell by 1.4% over the same period. The rate of loss slowed considerably in the second year, dropping to about 1% at the spine and 0.8% at the hip.
This bone loss translates into a real increase in fracture risk. Over a median follow-up of about five years, 7% of patients on exemestane experienced a fracture compared to 5% on tamoxifen. That said, no patient who entered the trial with normal bone density developed osteoporosis during treatment. Your starting bone health matters a lot.
To protect your bones while on exemestane, aim for at least 1,200 mg of calcium daily through food and supplements, and 400 to 800 IU of vitamin D per day (or 1,000 IU if you get very little sun exposure). Weight-bearing exercise, such as walking, light jogging, or resistance training, directly supports bone density and muscle strength. Even low-impact options like standing vibration platforms have shown measurable benefits in reducing spinal bone loss in postmenopausal women.
Cholesterol and Heart Health
Exemestane shifts your cholesterol profile in a way that deserves monitoring. In a direct comparison study, patients on exemestane saw their total cholesterol drop by about 8 mg/dL and their triglycerides decrease by 12 mg/dL, both positive changes. However, their HDL (“good”) cholesterol also fell by 8 mg/dL, and the ratio of LDL to HDL worsened significantly. That ratio is an important marker of cardiovascular risk.
Notably, patients who were already taking cholesterol-lowering medications were not protected from this HDL drop. If you have existing heart disease risk factors, your care team will likely want to check your lipid levels periodically while you’re on exemestane.
Sleep Problems, Mood Changes, and Brain Fog
Cognitive and sleep-related side effects are common across all aromatase inhibitors, and exemestane is no exception. A large study of over 1,000 breast cancer survivors taking aromatase inhibitors found that 52% reported insomnia, with about 20% experiencing moderate to severe sleep disruption. Nearly 80% reported at least one cognitive symptom: forgetfulness (74%), difficulty concentrating (58%), or feeling easily distracted (56%). Among those with cognitive complaints, almost half said their symptoms were at least moderately bothersome.
These numbers reflect the broader aromatase inhibitor class rather than exemestane alone, but the underlying mechanism is the same: estrogen influences sleep regulation and cognitive function, and suppressing it can disrupt both. Depression and anxiety have also been reported, though less systematically tracked in trials. If you notice a significant change in your mood, sleep quality, or mental sharpness after starting exemestane, it is a recognized effect of the drug, not something you’re imagining.
How Exemestane Compares to Other Aromatase Inhibitors
Exemestane is a steroidal aromatase inhibitor, which makes it structurally different from anastrozole and letrozole (both nonsteroidal). In practice, the side effect profiles overlap considerably, but there are some differences worth noting.
Fracture risk at five years is similar across all three drugs, hovering around 4.5% to 4.7%. The same is true for new-onset cholesterol problems, which developed in about 15.5% of exemestane patients versus 16% to 17% for the other two. Exemestane carried a slightly higher rate of diabetes (9.0% vs. 8.0% for anastrozole) in one large comparative analysis.
The most notable difference is discontinuation. About 39% of exemestane patients stopped treatment within five years, compared to 35% for both anastrozole and letrozole. That gap likely reflects the cumulative burden of side effects rather than any single issue. If side effects on one aromatase inhibitor become intolerable, switching to another is a common and often effective strategy, since individual responses vary considerably.
Taking Exemestane With Food
Exemestane absorbs significantly better when taken with food. A pharmacokinetic study found that eating a meal before taking the tablet increased the amount of drug absorbed by 1.6 times compared to taking it on an empty stomach. The good news is that this difference in absorption did not translate into a meaningful difference in how well the drug suppressed estrogen. Both fed and fasting states produced similar estrogen suppression. Still, the standard recommendation is to take exemestane after a meal to ensure consistent drug levels.
When Side Effects Tend to Peak
Most side effects are worst in the first three to six months. Hot flashes peak around month three. Overall quality of life tends to dip around the six-month mark and then recover. Joint symptoms can emerge within the first few weeks or develop gradually over months. Bone loss is steepest in the first six months and then slows. Understanding this timeline can help you push through an early rough patch that may well improve, though some effects like bone density changes require ongoing management for as long as you take the drug.