Estrogen can cause a wide range of side effects, from mild and temporary issues like nausea and breast tenderness to more serious risks like blood clots and certain cancers. The specific side effects you experience depend on the dose, how you take it (pill, patch, or gel), how long you use it, and why you’re taking it in the first place. Most common side effects improve within the first two months as your body adjusts.
Common Side Effects
The side effects most people notice first are the everyday physical ones. These include headaches, nausea or vomiting, stomach cramps and bloating, breast pain or tenderness, appetite and weight changes, and swelling in the hands, feet, or lower legs from fluid retention. Some people also experience back or pelvic pain, diarrhea, and vaginal bleeding or spotting.
Sleep disruption and emotional changes are also common. Insomnia, mood swings, and feelings of depression can develop, particularly in the early weeks of treatment. These effects are tied to the way estrogen interacts with brain chemistry. Estrogen influences several key chemical messaging systems in the brain, including those that regulate mood, reward, and calm. When estrogen levels shift rapidly, whether from starting therapy, changing doses, or stopping, this can destabilize those systems and increase vulnerability to anxiety or depressive symptoms.
Nausea tends to be the side effect that bothers people most when starting estrogen, but it’s usually self-limited and resolves within the first two months. Taking the medication with food and at bedtime can help. If nausea persists, switching from a pill to a patch often makes a significant difference because the estrogen bypasses the digestive system entirely.
Effects on Mood and Mental Health
Estrogen’s relationship with mood is complicated. At stable, moderate levels, estrogen generally has a protective effect on the brain. But severe fluctuations, especially during stressful periods, can increase the likelihood of depression, anxiety, and heightened stress responses. This helps explain why mood symptoms often cluster around times of hormonal transition, like starting or adjusting therapy.
There’s also a ceiling effect. Estrogen at doses higher than what the body would normally produce can actually worsen depressive symptoms by activating a different type of estrogen receptor in the brain. In some cases, adding estrogen to antidepressant therapy has triggered manic symptoms. This doesn’t mean estrogen therapy causes depression in most people, but it’s worth paying attention to mood changes, especially if you have a history of mood disorders.
Blood Clot and Stroke Risk
The most medically significant risk of estrogen therapy is venous thromboembolism (VTE), which includes deep vein blood clots and clots that travel to the lungs. For women not taking estrogen or hormonal birth control, the background risk is about 2 per 10,000 per year. Oral estrogen roughly doubles that risk or more, depending on the type and dose.
The type of estrogen matters. Synthetic estrogen (the kind in many older birth control formulations) carries a higher clot risk than natural estradiol. One large pooled analysis found a 33% lower risk of VTE with natural estradiol-based pills compared to synthetic estrogen pills. How you take it matters even more. Transdermal estrogen (patches and gels) carries substantially lower clot risk than oral forms. One study found a 56% reduction in clot risk with transdermal compared to oral estrogen. Another reported that oral estrogen nearly doubled VTE risk compared to transdermal routes.
Stroke risk follows a similar pattern. Oral estrogen at any dose increases stroke risk by about 25% to 48% compared to nonuse. Low-dose transdermal patches (50 micrograms or less per day) do not appear to increase stroke risk at all. High-dose patches, however, nearly doubled the risk. The stroke risk from oral estrogen also climbs with longer use (beyond five years), when started after age 60, and is notably higher in Black populations.
Dose matters across the board. A meta-analysis comparing low-dose and high-dose oral estrogen found that lower doses carried meaningfully less VTE risk. If you’re concerned about clotting, the general hierarchy of safety runs from low-dose transdermal (safest) to high-dose oral (highest risk).
Cancer Risk
Estrogen’s effect on cancer risk depends heavily on whether it’s taken alone or combined with a progestin, and on how long you take it.
Taking estrogen alone (without a progestin) for five or more years at least doubles the risk of uterine cancer. The risk increases further with longer use. This is why estrogen-only therapy is typically reserved for people who’ve had a hysterectomy. Adding a progestin to estrogen therapy eliminates this excess uterine cancer risk and actually reduces it by about 35% compared to taking no hormones at all.
The tradeoff is that combined estrogen-progestin therapy increases breast cancer risk. Data from the Women’s Health Initiative, one of the largest studies of hormone therapy ever conducted, found an absolute excess of 8 additional invasive breast cancers per 10,000 women per year attributable to combination therapy. That’s a real but relatively small absolute increase. Prolonged use beyond five years raises the risk further for both oral and transdermal forms, and both routes of administration carry similar breast cancer risk profiles.
Both oral and transdermal estrogen also modestly increase ovarian cancer risk. Neither form appears to affect the risk of developing type 2 diabetes.
Side Effects in Gender-Affirming Care
For transgender women and nonbinary people taking feminizing hormone therapy, the side effect profile overlaps with menopausal hormone therapy but includes additional effects. Decreased sex drive typically begins within one to three months and reaches its full effect by one to two years. Body fat redistribution starts at three to six months and continues for two to five years.
The cardiovascular risks are the same: blood clots, stroke, heart problems, and elevated triglycerides. Additional concerns in this population include high blood pressure, weight gain, elevated prolactin levels (which can occasionally cause nipple discharge), high potassium levels, and infertility. Type 2 diabetes risk may also increase.
Pills vs. Patches vs. Gels
The way you take estrogen shapes your side effect profile more than many people realize. Oral estrogen passes through the liver before reaching the rest of the body, which triggers changes in clotting factors, triglycerides, and other proteins. This “first-pass” liver effect is the main reason oral estrogen carries higher blood clot and stroke risk.
Transdermal estrogen (patches, gels, sprays) enters the bloodstream through the skin and largely bypasses the liver. This results in significantly lower clot and stroke risk, better tolerability for people prone to nausea or migraines, and a more physiologic hormone delivery pattern that mimics normal ovarian function. Oral estrogen does outperform transdermal forms in one area: it raises “good” HDL cholesterol and lowers “bad” LDL cholesterol more effectively. But it also raises triglyceride levels, which partially offsets that benefit.
Both routes reduce insulin resistance, with oral estrogen showing a slightly stronger effect in people without diabetes.
Managing Side Effects
Most common side effects can be managed by adjusting the dose, switching to a different preparation, or changing the route of administration. If breast tenderness, bloating, or nausea are persistent, a lower dose or a switch from oral to transdermal delivery often helps. For people who experience mood changes, adjusting the timing or type of progestin (if used) can sometimes make a difference.
The general principle is that lower doses and transdermal delivery carry fewer systemic side effects while still providing the intended benefits. For people at elevated baseline risk of blood clots, such as those who are obese, smoke, have a personal or family history of clotting disorders, or are over 60, transdermal estrogen is the preferred route.