Hormone replacement therapy can be very effective for menopausal symptoms, but like any treatment it has side effects, and the headlines about its risks have not always been balanced or accurate. This guide sets out what actually happens for most people: the common settling-in effects, which hormone tends to cause which, how long they usually last, and what the evidence says about the two risks people worry about most, breast cancer and blood clots. The aim is to give you the real picture in plain terms so that any decision you make with your clinician is an informed one. HRT is a personal choice, and for many women the benefits outweigh the risks, but that judgement depends on knowing what the risks genuinely are.
Common settling-in side effects
When you first start HRT, or change dose, it is common to notice some side effects as your body adjusts to the hormones. The reassuring part is that these are usually mild and tend to ease within about three months. Because HRT combines two different hormones for most women, it helps to separate the effects by which hormone tends to cause them, as the NHS guidance on HRT side effects does. That distinction matters, because if a particular effect is bothering you, changing the type or dose of that specific hormone is often the fix.
Oestrogen-related effects
Oestrogen is the hormone that does most of the work in relieving menopausal symptoms, and its common early side effects include breast tenderness or swelling, nausea, headaches, leg cramps and some fluid retention. These often settle as treatment continues. Taking oestrogen through the skin as a patch or gel, or taking a tablet with food, can help with nausea. If breast tenderness or headaches persist, a lower dose or a different preparation is often worth discussing.
Progestogen-related effects
Progestogen is included for women who still have a womb, to protect the lining from the effect of oestrogen. Its common side effects include bloating, breast tenderness, mood swings, low mood, acne and backache. Some women find the progestogen part harder to tolerate than the oestrogen, and in that case switching the type of progestogen, for example to one based on micronised progesterone, or changing how it is delivered, can make a real difference. Irregular or breakthrough bleeding is also common in the first few months of combined HRT and usually settles, but any bleeding that is heavy, persists beyond the settling-in period, or starts after a stable spell should always be checked by a clinician.
How long do side effects last?
As a general rule, give HRT around three months before judging how you feel on it. Most settling-in side effects fade over the first few weeks to months as hormone levels stabilise, and pushing through that early phase, where it is tolerable to do so, often means the side effects resolve while the benefits build. If side effects are still troubling you after three months, that is the point to review the dose, type or route rather than to assume HRT does not suit you. It is also worth remembering that some of what people attribute to HRT side effects is the menopause transition itself; our complete guide to perimenopause symptoms can help you tell the two apart.
The breast cancer evidence, in absolute terms
The link most people have heard about is between HRT and breast cancer, and it is real but often presented without the context that makes it meaningful. According to the NICE menopause guideline, oestrogen-only HRT is associated with little or no change in breast cancer risk. Combined HRT, which includes progestogen, can be associated with a small increase in risk, and that risk is related to how long HRT is taken and reduces after stopping. To put it in absolute terms, NICE illustrates that out of 1,000 women aged 50 to 59 not taking HRT, a certain number will be diagnosed with breast cancer over five years, and combined HRT adds a small number of extra cases on top of that baseline. For context, that additional risk is broadly comparable in scale to lifestyle factors such as being overweight or drinking a couple of alcoholic drinks a day. Framing it this way is not to dismiss the risk, but to size it honestly: for many women it is small relative to the benefit of symptom relief, and it is a personal balance to weigh with a clinician.
Blood clots and why the route matters
Blood clots are the other risk worth understanding, and here the way you take HRT makes a genuine difference. Oestrogen taken as a tablet is associated with a small increased risk of venous blood clots, because it is absorbed through the gut and passes through the liver, which affects clotting factors. Oestrogen absorbed through the skin, as a patch, gel or spray, largely bypasses that process, and current evidence indicates it is not associated with an increased risk of clots at standard doses. This is why NICE and menopause specialists often prefer transdermal oestrogen, especially for women who already have a higher baseline clot risk, for example due to weight, age or a personal or family history. It is one of the clearest examples of how the choice between patch and tablet is not just about convenience. Our complete guide to HRT patches looks at how the different routes compare in more detail.
The overall message on HRT side effects is a measured one. Most are mild, most settle within a few months, and many can be eased by adjusting the dose, hormone type or route rather than stopping altogether. The more serious risks are real but, for most women starting HRT around the time of menopause, smaller than the reputation suggests, and they vary with the type of HRT and how it is taken. None of this replaces a proper conversation with a GP or menopause specialist, who can weigh your own history and preferences. But going into that conversation knowing that the risks are usually modest, and that side effects are often adjustable, tends to make the decision feel a good deal clearer.
