The leaflet inside an HRT box lists everything anyone has ever reported while taking it, in no particular order, with no sense of which effects fade and which do not. It is a legal document rather than a guide. The predictable result is that a woman reads it, notices sore breasts in week three, decides HRT does not agree with her, and stops in month two, six weeks before the thing that bothered her would have settled on its own.
Most HRT side effects fall into one of three groups, and knowing which group you are dealing with changes what you should do about it. Some are the settling-in effects of the first three months. Some are a signal that the type, dose or route needs adjusting, which usually fixes them. And a small number mean you should be seen promptly.
Starting HRT means introducing a hormone your body has been managing without. There is an adjustment, and it usually announces itself in the same handful of ways:
The general rule offered by menopause specialists is to give a new regime around three months before judging it, unless something on the red flag list appears. Most of the above have either settled or clearly improved by then. What you should not do is stop and start repeatedly, because unstable levels tend to produce worse symptoms than either taking it or not.
This depends entirely on which regime you are on, and a lot of unnecessary alarm comes from not being told which one you have.
On sequential HRT, usually prescribed when you still have periods, a monthly withdrawal bleed is the intended outcome, not a side effect.
On continuous combined HRT, prescribed once you are past menopause, the aim is no bleeding at all. But unpredictable spotting and light bleeding in the first three to six months is common and expected, and it is not a sign that something is wrong.
What needs looking at rather than waiting out: bleeding that is still unpredictable after six months, bleeding that starts again after a settled period of nothing, bleeding that is heavy, and any bleeding after sex. None of these mean something sinister is happening, and most turn out to be a polyp, a dose issue or absorption. They do mean you need an appointment rather than patience.
Women who tell their GP that HRT makes them feel awful are usually describing the progestogen part. If you still have a womb you need it, because it protects the womb lining from unopposed oestrogen, but which one you take is far from fixed.
The classic pattern is a recognisable, cyclical version of PMS: low mood, irritability, bloating, tearfulness, sore breasts, arriving reliably during the progestogen phase and lifting when it stops. If your symptoms have a rhythm, that rhythm is diagnostic.
There are usually options. Micronised progesterone, which is body-identical, tends to be better tolerated than older synthetic progestogens and has the useful side effect of being mildly sedating, so it is taken at night. The levonorgestrel intrauterine system delivers progestogen locally to the womb lining with far less reaching the rest of you, which suits women who cannot tolerate it any other way. Dose and duration can also be adjusted. PMS vs PMDD is worth reading if this pattern is familiar from before HRT, because women with a history of severe premenstrual symptoms are more likely to run into it.
Oestrogen through the skin and oestrogen swallowed are not equivalent, and the difference is not a preference.
Clot risk. Oral oestrogen passes through the liver first and raises the risk of venous thromboembolism. Transdermal oestrogen, in patches, gels and sprays, is not associated with an increased clot risk at standard doses. This is why transdermal is the usual first choice, and why it remains an option for women with risk factors who might otherwise be told HRT is closed to them.
Migraine. Migraine with aura rules out the combined contraceptive pill, and a great many women are wrongly told this rules out HRT too. It does not. Transdermal oestrogen delivers steadier levels, and steady levels are what migraine-prone brains prefer. Hormonal headaches and migraines goes through this in detail.
Libido. A less discussed one. Oral oestrogen raises sex hormone binding globulin, which mops up circulating testosterone and can leave less of it available. If your libido has dropped since starting oral HRT, that is a plausible mechanism and a reason to discuss switching route. Low libido in midlife covers the wider picture.
Absorption. Patches can fail to stick in hot weather or after swimming. Gel needs a few minutes to dry and should not be applied straight before dressing. Symptoms that improve then return can be an absorption story rather than a dose story.
Testosterone is prescribed for some women, most often for persistent low libido once oestrogen has been optimised, and it is used off-label in the UK. Its side effects are dose-dependent and mostly avoidable: acne, oilier skin, and increased hair growth at the site where the gel is applied. This is why it should be prescribed at a female physiological dose and monitored with blood tests rather than issued and forgotten. Testosterone in women covers what it does and does not do.
Weight gain. This is the single most common reason women refuse HRT, and the evidence does not support it. Weight tends to rise in midlife whether or not a woman takes HRT, and body fat redistributes towards the middle as oestrogen falls, which is a separate process. Does HRT cause weight gain? goes through the trial data, and why weight gathers around your middle explains the mechanism.
Early fluid retention is real and can shift the number on the scales in the first weeks. It is not fat, and it usually settles.
Vaginal oestrogen belongs in a category of its own. Very little is absorbed into the bloodstream, the side effect profile is minimal, it can be used long-term, and it can be used alongside systemic HRT or on its own. Many women who need it are not offered it. See vaginal dryness and intimacy.
Breast cancer risk is the question underneath most others, and it is a different kind of consideration from sore breasts in week three. In short: oestrogen-only HRT, taken by women without a womb, carries little or no increased risk. Combined HRT carries a small increase that relates to how long you take it, and for many women it is smaller than the risk attached to drinking a couple of glasses of wine most nights or carrying excess weight. It is a real number to weigh, not a reason for blanket fear, and the truth about the HRT research unpacks where the original scare came from.
These are uncommon. They are on the list because acting quickly matters more than being certain.
Change one thing at a time, and give it long enough to tell you something. Most problems resolve by adjusting the oestrogen dose, changing the route from tablet to patch or gel, switching the progestogen or its schedule, or fixing an absorption habit. What tends not to work is stopping altogether and concluding HRT is not for you, when the first combination you were handed was a starting point rather than a verdict.
Go to the appointment with a written record of what happens and when, because "I feel awful" and "it starts on day fourteen and lifts on day twenty-six" lead to completely different conversations. The free hormone tracker is built for exactly this, and the HRT checker will produce a tailored list of questions to take with you.
How long do HRT side effects last?
Most settling-in effects improve within three months. Anything still troubling you after that is usually a sign the type, dose or route needs adjusting rather than a reason to stop.
Is bleeding on HRT normal?
On sequential HRT a monthly bleed is intended. On continuous combined HRT, unpredictable spotting in the first three to six months is common, but bleeding after six months, or bleeding that restarts, needs investigating.
Can I take HRT if I get migraines?
Usually yes, including migraine with aura, which rules out the combined pill but not HRT. Transdermal oestrogen is preferred because it gives steadier levels.
Which HRT has the fewest side effects?
There is no universal answer, but transdermal oestrogen with micronised progesterone is the combination most often reached for when tolerability is the priority.
Sources: NICE NG23, Menopause: diagnosis and management · British Menopause Society, Prescribable alternatives and HRT preparations consensus statements · Vinogradova Y et al., Use of hormone replacement therapy and risk of venous thromboembolism, BMJ 2019;364:k4810 · Collaborative Group on Hormonal Factors in Breast Cancer, Lancet 2019;394:1159-68 · Educational only, not medical advice.
Keep reading: HRT explained · What age does menopause start? · The truth about the HRT research · Does HRT cause weight gain? · Hormonal headaches and migraines · Check your HRT fit (free) · Take the free Hormone Quiz