Menopausal symptoms can range from the very mild, to severe and disabling.
Vasomotor symptoms – hot flushes and sweats – are the commonest symptom, but are frequently accompanied by others such as fatigue, mood changes, insomnia, reduced libido, urinary and vaginal symptoms.
HRT (hormone replacement therapy) improves these symptoms, with the strongest evidence of its effect being on vasomotor symptoms.
Menopausal symptoms will improve or disappear over time, though there is huge variation in their duration:
In a study of 881 women in the US, the median duration of hot flushes was 7.4 years.
HRT has some other associated long-term benefits and harms. Most of these are small in absolute terms, with breast cancer risk being the most significant.
The choice to take HRT (including what type and how long to take it for) involves a consideration of the benefits on symptom relief against potential long-term benefits and harms, and is very much down to the individual.
Individuals will have differing frequency and severity of hot flushes, and differing response to HRT.
On average, randomised controlled trials show that:
Figures derived from:
Both compared oestrogen-containing (with or without progesterone) HRT to placebo.
References
1)Avis NE, Crawford SL, Greendale G et al. Study of Women’s Health Across the Nation. Duration of menopausal vasomotor symptoms over the menopause transition. JAMA Intern Med 2015; 175(4): 531-539
2)MacLennan AH, Broadbent JL, Lester S, Moore V. Oral oestrogen and combined oestrogen/progestogen therapy versus placebo for hot flushes. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD002978
3)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015 [updated 2019]. (NICE Guidleine [NG23])
| This research provides some indication of the treatment effect.
There is a high possibility that the true effect is smaller or greater. |
NICE rated this evidence as LOW quality1:
Reference
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015 [updated 2019]. (NICE Guidleine [NG23])
The studies reported in the Cochrane review1 had the following characteristics:
The NICE review did not summarise the population characteristics.
Reference
1)MacLennan AH, Broadbent JL, Lester S, Moore V. Oral oestrogen and combined oestrogen/progestogen therapy versus placebo for hot flushes. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD002978
Menopause is associated with a wide range of symptoms in addition to hot flushes.
Despite anecdotal evidence that HRT can improve many symptoms, there is limited RCT evidence to support this. This may well be due to under-research and lower quality trials.
Anxiety and low mood
The NICE evidence review found one MODERATE quality trial reporting a statistically significant improvement in anxiety and low mood:
A number of smaller and lower quality trials did not find any benefit on these outcomes.
Musculoskeletal symptoms
The NICE evidence review found two trials of MODERATE quality which did not show any benefit from HRT compared to placebo on this outcome:
Sexual function
A 2013 Cochrane review2 found that for women with menopausal symptoms, oestrogen (with or without progesterone) provided:
References
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015 [updated 2019]. (NICE Guidleine [NG23])
2)Nastri CO, Lara LA, Ferriani RA et al. Hormone therapy for sexual function in perimenopausal and postmenopausal women. Cochrane Database of Systematic Reviews 2013, Issue 6. Art. No.: CD009672
Side effects were poorly reported in the RCTs in the Cochrane review1, and they were unable to give summary statistics for these.
Breast tenderness was the commonest reported side effect, with very roughly 1 in 5 women reporting this with HRT.
Oedema, joint pain and psychiatric symptoms were reported as “recurrent” reasons for treatment withdrawal, however:
No serious adverse events were reported.
Data on long-term risks are presented in the sections below.
Reference
1)MacLennan AH, Broadbent JL, Lester S, Moore V. Oral oestrogen and combined oestrogen/progestogen therapy versus placebo for hot flushes. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD002978
Vaginal oestrogen preparations are effective in relieving symptoms of postmenopausal vulvovaginal atrophy.
This affects up to 50% of women and typically presents 4 to 5 years after the menopause.
Topical oestrogen may be used alone or as an adjunct to systemic HRT.
The table below summarises the number of women reporting improvement in a range of symptoms:
| Treatment duration | Placebo preparation | Topical oestrogen | |
| Overall symptoms | 3 months | 22% | 46% |
| Vaginal dryness | 1 year | 28% | 84% |
| Dyspareunia | 1 year | 27% | 73% |
| Itching and/or discomfort | 1 year | 37% | 80% |
Vaginal oestrogen safety and side effects
Newer agents: prasterone and ospemifene
more
Vaginal prasterone is recommended in the 2024 NICE guideline if topical oestrogen is ineffective or not tolerated.
Oral ospemifene is recommended if the use of locally applied treatments is impractical, for example, because of disability.
Both these treatments were found to be roughly as clinically effective as vaginal oestrogen, but less cost-effective3.
No increase in side-effects or harms was found in the NICE evidence review, though studies were all short-term.
Figures for vaginal oestrogen derived from the 2015 NICE evidence review2.
For prasterone and ospemifene, NICE conducted a network meta-analysis in 2024. This consisted of 40 studies comparing a variety of treatments for genitourinary symptoms associated with menopause3.
References
1)HRT guide for health professionals. British Menospase Society. Accessed online Jan 2023.
2)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guideline [NG23])
3)National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23]
| This research provides a good indication of the treatment effect.
There is a moderate possibility that the true effect is smaller or greater. |
NICE rated the evidence for vaginal oestrogen as MODERATE quality:
However,
Reference
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guideline [NG23])
The characteristics of the patients in these studies on vaginal oestrogen were summarised by NICE as:
Reference
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guidleine [NG23])
Menopause-specific Cognitive Behavioural Therapy (CBT) is recommended in the 2024 NICE guideline.
Consider it as an option. It may help with menopausal symptoms as either a stand-alone treatment or alongside HRT.
CBT may
NICE’s evidence review showed that menopause-specific CBT did not improve
How big were the benefits of CBT?
more
There was a big range in the size of benefits shown for CBT between studies. Some showed very little benefit. Examples of the biggest effects are:
Figures derived from 2024 NICE evidence review1:
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
| This research provides some indication of the treatment effect.
There is a high possibility that the true effect is smaller or greater. |
NICE rated most of the evidence as very low or low quality
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
The population characteristics in the trials in the NICE review were:
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
Testosterone as an addition to oestrogen-containing HRT has been shown to improve sexual function in women who report low libido or sexual dysfunction during or after menopause.
The table below summarises these improvements as compared to placebo.
| Standardised mean difference in sexual function score* | +0.25 approx | This represents a small but meaningful improvement. |
| Number of satisfactory sexual events (SSE) per month | +1 approx | In the study populations, the baseline number of SSE was about 1-3 per month |
*The most common scoring system used in the studies was the PFSF, which gathers self-reported assessments across a number of domains: desire, arousal, orgasm, pleasure, concerns, responsiveness, self-image.
There is no RCT data to show an improvement in cognition or musculoskeletal function.
There is no long term data regarding outcomes such as cardiovascular events, fracture or cancers.
Harms of testosterone therapy
Excess hair growth
2.4% of women in the RCTs developed excess hair growth due to testosterone therapy:
Acne
2.5% of women in the RCTs developed acne due to testosterone therapy:
LDL cholesterol changes
Transdermal testosterone therapy was not associated with any rise in LDL in the RCTs.
Oral testosterone therapy was associated with an average rise in LDL of 0.29mmol/mol compared to placebo.
Figures derived from a 2019 systematic revew1, which has similar findings to the 2015 NICE evidence review2:
References
1)Islam RM, Bell RJ, Green S et al. Safety and efficacy of testosterone for women: a systematic review and meta-analysis of randomised controlled trial data. The Lancet Diabetes & Endocrinology 2019; 7(10): 754-766
2)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guideline [NG23])
| This research provides some indication of the treatment effect.
There is a high possibility that the true effect is smaller or greater. |
This evidence rates as LOW quality:
However,
Reference
1)Islam RM, Bell RJ, Green S et al. Safety and efficacy of testosterone for women: a systematic review and meta-analysis of randomised controlled trial data. The Lancet Diabetes & Endocrinology 2019; 7(10): 754-766
The population characteristics in the trials in this systematic review were, roughly:
Reference
1)Islam RM, Bell RJ, Green S et al. Safety and efficacy of testosterone for women: a systematic review and meta-analysis of randomised controlled trial data. Lancet Diabetes & Endocrinology 2019; 7(10): 754-766
The 2015 NICE evidence evidence review found some evidence of benefit on reduction of hot flushes with:
The recommendations to consider these treatments comes with a caveat that there is variation/uncertainty in the composition of various products available, so any effect is uncertain.
Source: MHRA
No statistically significant evidence of benefit was found for:
Reference
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015 [updated 2019]. (NICE Guideline [NG23])
HRT increases the risk of breast cancer. Absolute risk may be small and depends on type and duration of HRT use:
Though the incidence of breast cancer is increased, no increase in breast cancer mortality has been shown with HRT use.
The figures and graphics below represent someone who starts HRT at age 50.
Figures derived from the evidence review for the 2024 NICE guideline1
The review included findings from
Data detail
The figures for the graphics above were taken from data tables presented in the main NICE guideline.
NICE used the relative risks for breast cancer from observational studies, and combined those with age-specific incidence rates for breast cancer from the Office for National Statistics to produce these illustrative figures.
References
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
2) Collaborative Group on Hormonal Factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence The Lancet 2019; 394( 10204): 1159-1168
| This research provides a good indication of the treatment effect.
There is a moderate possibility that the true effect is smaller or greater. |
NICE rated elements of the evidence in this review from VERY LOW to HIGH but were of the view that overall, the observational data gave reliable enough information to inform patients about risks associated with HRT1.
Previous and other estimates of risk, including those based on RCTs alone, have been slightly different but are essentially in the same ballpark as these figures2-4.
The imperfect nature of the evidence base means there will always be some uncertainty and controversy about the exact size of these risks.
References
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
2)MHRA. Hormone replacement therapy (HRT): further information on the known increased risk of breast cancer with HRT and its persistence after stopping. Drug Safety Update. Aug 2019.
3)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. Ch.11.5.7 (NICE Guideline [NG23])
4)Marjoribanks J, Farquhar C, Roberts H, Lethaby A, Lee J. Long‐term hormone therapy for perimenopausal and postmenopausal women. Cochrane Database of Systematic Reviews 2017, Issue 1. Art. No.: CD004143.
The wide range of studies in this NICE evidence review1 included:
References
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
2) Chlebowski RT, Anderson GL, Aragaki AK et al. (2020) Association of Menopausal Hormone Therapy with Breast Cancer Incidence and Mortality during Long-term Follow-up of the Women’s Health Initiative Randomized Clinical Trials. JAMA. 324(4): 369-380
When thinking about breast cancer risk with HRT, it may be useful to put this risk into perspective.
A 2017 British Menopause Society publication1 presented data on lifestyle factors and their impact on breast cancer risk. The magnitude of these risks is broadly similar to that associated with HRT:
|
Number of cases of breast cancer in general population without these lifestyle factors: 23 per 1000 women over 5 years |
||||
| Lifestyle factor | Alcohol consumption
>2 units per day |
Smoking | Obesity
BMI >30kg/m2 |
Moderate exercise >2 1/2 hours per week |
| Change in number of cases per 1000 women over 5 years with this lifestyle factor |
+5 | +3 | +24* | -7 |
| Number of cases of breast cancer in population with this lifestyle factor per 1000 women over 5 years |
28 | 26 | 47 | 16 |
* Obesity and HRT risk. One finding from the recent epidemiological study2 providing the main figures for breast cancer risk in this section, was that:
Reference
1)British Menopause Society. Understanding the risks of breast cancer. Infographic 2017. Accessed online Jan 2023
Note: (1) We have not reviewed the evidence behind this infographic; and (2) it contains estimates for breast cancer risk which are lower and based on past evidence.
2)Collaborative Group on Hormonal Factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence. Lancet 2019; 394(10204): 1159-1168
Continuous combined regimens of oestrogen and progesterone are associated with higher rates of breast cancer than those where progesterone is taken cyclically.
These figures from the major study in the NICE evidence review give an idea of the difference:
| Cumulative cases of breast cancer per 1000 women over 20 years | |||
| No HRT use | 5 years HRT use | 10 years HRT use | |
| Sequential Combined HRT | 63 | 77 | 92 |
| Continuous Combined HRT | 63 | 83 | 103 |
Note: the figures here for “No HRT use” are different from the main data graphics on this website because the reference populations were different in this study compared to the overall NICE analysis
Reference
1)Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence. The Lancet, Volume 394, Issue 10204, 1159 – 1168
The 2024 NICE review concluded that there was not strong enough evidence to support the claim that transdermal HRT preparations are associated with a lower risk of breast cancer.
Though some studies have suggested a lower risk (when looking at combined HRT), others have not. Overall, the evidence is inconclusive.
Reference
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
In recent years in the UK, the use of micronised progesterone as a component of combined HRT has increased due to evidence that it may be associated with less breast cancer risk than other progestogens. The British Menopause Society (BMS) supports that view1.
The 2024 NICE guideline does not recommend micronised progesterone in place of other progestogens. NICE’s interpretation of the evidence is that it is not strong enough and recommends further research.
Why the disagreement?
The BMS view is underpinned by a large observational study from France2, where micronised progesterone has been in common use for much longer.
This study found that:
The NICE committee found that when analysed with other data in their review, the confidence intervals around the French data had enough overlap with other studies on different progestogens that they could not be certain enough to make a specific recommendation for any type of progesterone.
The BMS continues to argue in favour of micronised progesterone and questions whether NICE took enough account of the French data3.
References
1)British Menopause Society. BMS & WHC’s 2020 recommendations on hormone replacement therapy in menopausal women [online]. London 2020. Accessed 17/1/2025
2)Fournier A, Mesrine S, Dossus L et al. Risk of breast cancer after stopping menopausal hormone therapy in the E3N cohort. Breast Cancer Res Treat. 2014 Jun;145(2):535-43.
3)British Menopause Society. BMS statement in response to the publication of the updated NICE Menopause guideline (NG23) [online]. London 2024. Accessed 17/1/2025
Concern that HRT might increase the risk of cardiovascular disease was raised after the publication of data from the Women’s Health Initiative study in 2003 which looked predominantly at women starting HRT in their mid-60s.
The 2024 NICE evidence review found HRT to be generally safe from a cardiovascular perspective, but showed small increases in stroke and VTE risk with oral preparations:
These figures from the NICE evidence review refer to women aged 50 on starting HRT:
| No HRT
Events per 1000 women over 5 years |
HRT use
Events per 1000 women over 5 years |
Absolute difference per 1000 women over 5 years | |
| Coronary Heart Disease | |||
| All types of HRT | 9 | 9 | None |
| Stroke | |||
| Transdermal HRT | 3 | 3 | None |
| Oral HRT | 3 | 4 | 1 more |
| Venous Thromboembolism | |||
| Transdermal HRT | 12 | 12 | None |
| Oral HRT | 12 | 22 | 10 more |
Figures for CHD and Stroke derived from the 2024 NICE evidence review1.
Figures for VTE derived from the 2015 NICE evidence review2.
Data detail
The figures in the table above were taken from data presented in discussion aid accompanying the main NICE guideline.
NICE used the relative risks for vascular disease from their evidence review and combined those with age-specific baseline incidence rates from the Office for National Statistics to produce these illustrative figures.
References
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
2) National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guideline [NG23])
| This research provides some indication of the treatment effect.
There is a high possibility that the true effect is smaller or greater. |
NICE found the evidence quality in this review ranged from VERY LOW – HIGH with most of the evidence being LOW quality:
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
Most studies in the NICE evidence review were conducted in Europe, North America and Australasia. Summary data on the study population was not provided.
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
HRT has effects on the incidence of endometrial cancer. These vary according to the presence of progesterone.
| Rates of endometrial cancer per 1000 women aged 50-54 | |||
| No HRT | HRT use | Absolute difference | |
| Continuous combined HRT | 4 | 1 | 3 fewer |
| Sequential combined HRT | 4 | 8 | 5 more |
| Oestrogen only HRT | 4 | 11 | 7 more |
Figures derived from the 2024 NICE evidence review1.
Data detail
The figures in the table above were taken from data presented in discussion aid accompanying the main NICE guideline.
NICE used the relative risks for endometrial cancer from representative studies in their evidence review and combined those with age-specific baseline incidence rates from the Office for National Statistics to produce these illustrative figures.
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
| This research provides a very good indication of the treatment effect.
However, it is possible that the true effect is slightly smaller or greater. |
NICE reviewed a large body of evidence and selected HIGH quality studies from within that to derive risk estimates. These were:
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
The study population in the studies used to generate the risk estimates were:
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
There is a small increased risk of ovarian cancer associated with HRT.
| Rates of ovarian cancer per 1000 women aged 50-54 | |||
| No HRT | HRT use | Absolute difference | |
| Any HRT ~5 years duration | 1 | 2 | 1 more |
Figures derived from a 2024 NICE evidence review.
Data detail
The figures in the table above were taken from data presented in discussion aid accompanying the main NICE guideline.
NICE combined two data sources to produce these illustrative figures:
relative risk for ovarian cancer from one individual-patient-data meta-analysis(2) included in the NICE review, combined with
age-specific baseline incidence rates from the Office for National Statistics.
References
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
2) Collaborative Group on Hormonal Factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence The Lancet 2019; 394( 10204): 1159-1168
| This research provides a very good indication of the treatment effect.
However, it is possible that the true effect is slightly smaller or greater. |
NICE reviewed a large body of evidence of variable quality, and selected one HIGH quality meta-analysis to derive risk estimates.
References
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
2) Collaborative Group on Hormonal Factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence The Lancet 2019; 394( 10204): 1159-1168
The study population in the studies used to generate the risk estimates were:
Reference
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
HRT improves bone density and reduces fracture risk whilst it is being taken. But this benefit decreases after treatment stops.
| Rates of fracture per 1000 women | ||||
| No HRT | Current HRT use | Absolute reduction | Long term after stopping HRT
(approximately > 5 years after*) |
|
| Between ages 50-54 | 60 | 40 | 20 fewer | No significant difference to women not taking HRT |
| Between ages 50-59 | 127 | 80 | 47 fewer | |
*in the 2015 evidence review, NICE gave this 5-year period as an estimate for the time taken to lose fracture protection after stopping HRT. However, in the 2024 update, the guideline committee felt that the evidence around this timeline was unclear so changed the phrasing to simply “…this benefit decreases when treatment stops”.
Figures derived from 2015 and 2024 NICE evidence review.1,2
Data detail
The 2024 guideline did not involve an updated evidence review, but drew on the 2015 estimates of fracture risk reduction and used ONS data for background “no HRT” fracture risk estimates.
References
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guideline [NG23])
2) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
| This research provides some indication of the treatment effect.
There is a high possibility that the true effect is smaller or greater. |
NICE rated this evidence quality as LOW
Reference
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guideline [NG23])
Details of the study population characteristics were not summarised in the NICE review1 except that the participants were post-menopausal women age 45-69.
Reference
1)National Institute for Health and Care Excellence. Menopause: diagnosis and management [Internet]. [London]: NICE; 2015. (NICE Guideline [NG23])
NICE reviewed evidence for the effect of HRT on both dementia and all-cause mortality for their 2024 guideline1.
They concluded that there was insufficient or uncertain evidence about these outcomes, and the majority of evidence showed no significant difference between users and non-users of HRT.
On dementia specifically:
References
1) National Institute for Health and Care Excellence. Menopause: diagnosis and management. Appendix A [Internet]. [London]: NICE; 2024. (NICE Guideline [NG23])
2) Shumaker, Sally A, Legault, Claudine, Kuller, Lewis et al. Conjugated equine estrogens and incidence of probable dementia and mild cognitive impairment in postmenopausal women: Women’s Health Initiative Memory Study. JAMA 2004; 291(24): 2947-58
People who have an adverse event
People whose adverse event is prevented by treatment
People who were never going to have an adverse event anyway
Graphics and NNTs are rounded to the nearest integer
These three statistical terms offer three different ways of looking at the results of trial data.
Absolute Risk Reduction
This tells you how many people out of 100 who take a treatment have an adverse event prevented.
MoreThe value of the ARR changes with the baseline risk of the person (or population) taking the treatment. The higher the starting risk, the greater the absolute chance of benefit.
You need to think about over what time the trial data show this benefit, as it is usually assumed that more absolute risk reduction is gained over time.
Your patient might be taking the treatment for much longer than the length of a clinical trial (or, if life expectancy is limited, perhaps for less time).
Number Needed to Treat
This tells you how many people need to take the treatment in order for one person to avoid an adverse event.
The lower the number, the more effective the treatment.
MoreThe value of the NNT changes with the baseline risk of the person (or population) taking the treatment. The higher the starting risk, the smaller the NNT.
You need to think about over what time the trial data show benefit, as it is usually assumed that more benefit is gained over time and therefore the NNT will drop over time.
Your patient might be taking the treatment for much longer than the length of a clinical trial (or, if life expectancy is limited, perhaps for less time).
Relative Risk Reduction
This tells you the proportion of adverse events that are avoided if the entire population at risk is treated.
MoreThe value of the RRR is usually constant in people (or populations) at varying degrees of risk.
It is also usually assumed to stay constant over time.
This can be helpful, especially when thinking about population outcomes, but can be misleading for an individual person:
For example, a RRR of 25% in someone with a baseline risk of 40% would give them an ARR of 10% and an NNT of 10.
A RRR of 25% in someone with a baseline risk of 4% would give them an ARR or 1% and an NNT of 100.
This website is designed for use by General Practitioners and other healthcare professionals. The content is not exhaustive and assumes a standard level of GP professional knowledge. The information here is intended to support clinical judgement and shared decision making alongside clinical guidelines and standard practice.
If you are a patient/member of the public, do feel free to look around, but please don’t make any changes to your treatments based on information here. If you find something which seems relevant to you, you could show this website to your healthcare professional to help a discussion.