The most common side effects of HRT are breast tenderness, headaches, nausea, bloating, and irregular vaginal bleeding. Most of these appear within the first few weeks of starting treatment and improve within the first three months as your body adjusts to the new hormone levels. Understanding which side effects are temporary, which depend on your type of HRT, and which deserve attention can make a real difference in how you experience treatment.
Estrogen-Related Side Effects
Estrogen is the core component of most HRT regimens, and it’s responsible for the side effects new users notice first. Breast tenderness and swelling are among the earliest to appear, often starting within days. Headaches, nausea, and bloating are also common in the initial weeks. Fluid retention can make you feel puffy or heavier, particularly around the ankles, hands, and abdomen. Some women also experience leg cramps or indigestion.
These symptoms are your body’s response to a sudden rise in estrogen after a period of decline. They typically settle down within the first few months of treatment. If they persist beyond that window, adjusting the dose or switching to a different form of estrogen often helps.
Progestogen-Related Side Effects
If you still have your uterus, your HRT will include a progestogen alongside estrogen. This protects the uterine lining, but it comes with its own set of side effects that can feel a lot like premenstrual symptoms. Mood changes, including irritability, low mood, or anxiety, are among the most commonly reported. Breast tenderness, acne, bloating, and back pain can also occur.
Irregular vaginal bleeding or spotting is particularly common during the first three to six months of combined HRT. This is one of the side effects that most alarms new users, but it’s expected during the adjustment period. The type of progestogen in your HRT matters too. Different formulations have slightly different side effect profiles, so switching the progestogen component is a standard strategy if side effects linger.
Mood Changes and Emotional Effects
Both estrogen and progestogen can affect mood, which makes this one of the trickier side effects to sort out. Some women feel more anxious, irritable, or emotionally flat after starting HRT. For others, HRT dramatically improves the low mood and anxiety that came with perimenopause in the first place.
The challenge is that perimenopause itself causes mood disruption. Up to 10% of women experience clinical depression during perimenopause, driven by unstable estrogen levels. So when mood symptoms appear after starting HRT, it can be genuinely difficult to tell whether you’re experiencing a side effect of the medication or a symptom that the current dose isn’t fully treating. If your mood worsens or doesn’t improve after the first few months, it’s worth revisiting the type, dose, or delivery method with your prescriber rather than assuming HRT simply isn’t working.
Weight Gain: Side Effect or Coincidence?
Weight gain is one of the most common fears people have about starting HRT, but the evidence doesn’t support it as a direct side effect. Menopause itself slows your resting metabolic rate, meaning your body burns fewer calories at rest than it used to. Weight gain tends to be greatest during the perimenopausal years regardless of whether you take HRT. There’s also a shift in where fat accumulates, with more settling around the midsection rather than the hips and thighs.
Some HRT regimens may actually help counteract this. Research has found that certain estrogen-progestogen combinations can reduce the increase in body fat and the shift toward abdominal fat storage that comes with menopause. The fluid retention that occurs in early treatment can cause the number on the scale to rise by a few pounds, which is often mistaken for fat gain. This water weight typically resolves as your body adjusts.
How Your Delivery Method Changes the Picture
The way you take HRT significantly affects which side effects you’re likely to experience. Oral tablets pass through the liver before reaching the rest of your body, and this “first pass” effect is responsible for several of the more serious risks. Oral estrogen roughly doubles the risk of blood clots compared to not taking HRT. Estrogen-only oral therapy raises that risk by about 50%.
Transdermal options, meaning patches, gels, or sprays applied to the skin, bypass the liver entirely. Studies show no clear increase in blood clot risk, stroke risk, or heart disease risk with transdermal estrogen. Clinical guidelines now recommend transdermal HRT over oral for women who have elevated risk for blood clots, gallstones, stroke, or cardiovascular disease. Transdermal delivery also tends to cause less nausea and fewer digestive issues, since the hormones aren’t passing through your gut.
Vaginal estrogen, used specifically for urogenital symptoms like dryness or discomfort, delivers such low systemic doses that side effects are minimal and largely limited to local irritation.
Testosterone Therapy Side Effects
Some HRT regimens include low-dose testosterone, typically for low libido or fatigue that estrogen alone doesn’t resolve. Testosterone increases your skin’s oil production, which can lead to acne on the lower face, chest, upper arms, and back. This acne often appears within the first two years and can be persistent, sticking around as long as testosterone therapy continues. Reducing the dose doesn’t necessarily clear it up.
Other androgenic effects can include increased facial or body hair growth and, less commonly, thinning of scalp hair. These effects tend to be dose-dependent, though individual sensitivity varies widely.
The Adjustment Period
Most common side effects follow a predictable arc. They appear within the first few weeks, peak in intensity, and then gradually fade as your body acclimates to the new hormone levels. The NHS advises that headaches, breast tenderness, and vaginal bleeding typically improve within the first few months. Three months is the standard timeframe clinicians use before making dose adjustments, because changing things too early can reset the adjustment clock.
If side effects haven’t improved after three months, there are several practical levers to pull: changing the dose, switching from oral to transdermal delivery, trying a different progestogen, or altering the schedule (continuous versus cyclical). Many women try two or three combinations before finding one that controls their menopause symptoms without bothersome side effects.
Sorting Side Effects From Untreated Symptoms
One of the most confusing aspects of starting HRT is that some side effects overlap with the menopause symptoms you’re trying to treat. Headaches, mood changes, sleep disruption, and bloating can all be caused by HRT or by menopause itself. The timing is the biggest clue. If a symptom appears for the first time after starting HRT or gets noticeably worse, it’s more likely a side effect. If it was already present and hasn’t improved, the dose or formulation may need adjusting.
Keeping a simple symptom diary for the first few months, noting what you feel and when, gives you and your prescriber much better information to work with than trying to reconstruct weeks of vague impressions from memory.