Hormonal Contraception
The pill, the coil, the implant — and the gap between 'over 99%' and what actually happens
The evidence base is large and mature. Hormonal contraception is highly effective and, for most people, safe. Confidence is high on efficacy, on the venous thromboembolism risk of the combined pill, on the stroke contraindication in migraine with aura, and on the substantial long-term reduction in ovarian and endometrial cancer. The genuinely unsettled question is mood, where an association exists and causality is contested.
How confident is BioSignal?
Our overall position, and how sure we are of it across each dimension — including where we are not sure at all.
High confidence
The evidence base is large and mature. Hormonal contraception is highly effective and, for most people, safe. Confidence is high on efficacy, on the venous thromboembolism risk of the combined pill, on the stroke contraindication in migraine with aura, and on the substantial long-term reduction in ovarian and endometrial cancer. The genuinely unsettled question is mood, where an association exists and causality is contested.
Well-supported by consistent, high-quality evidence.
Biological Role
Well characterised. Combined methods suppress ovulation; progestogen-only methods thicken cervical mucus, thin the endometrium and often suppress ovulation; the copper IUD is non-hormonal and spermicidal.
Human Evidence
Decades of use, large cohort studies and randomized data across hundreds of millions of users. Few interventions have been observed at this scale.
Clinical Benefit
Highly effective at preventing pregnancy, with large differences between methods in TYPICAL use. Also genuinely therapeutic for heavy bleeding, endometriosis pain and acne.
Broader Claims
The non-contraceptive effects are real and mixed: substantial reduction in ovarian and endometrial cancer, small increase in breast cancer while using, contested effects on mood.
Safety Confidence
Safe for the great majority. The risks are specific, identifiable and largely avoidable by choosing the right method — VTE with combined methods, and the absolute stroke contraindication in migraine with aura.
Research Activity
Active work on mood effects, on male contraception, and on non-hormonal alternatives. The core efficacy and safety questions are settled.
Where the evidence stands today
How mature the science is, what kinds of evidence exist, and — the part nobody else prints — what is still missing.
9/9
steps proven in humans
Evidence-rich
Proven at every applicable step — rare, and worth noticing.
Guideline / regulatory support
ProvenLARC first-line for effectiveness; migraine with aura an absolute contraindication to combined methods.
Clinical outcomes
ProvenPregnancy, VTE, stroke, and cancer incidence — hard outcomes, at scale.
Large human RCTs
ProvenRandomized data on efficacy and on comparative methods.
Small human outcome trials
ProvenSuperseded by large-scale data.
Human safety data
ProvenVTE, stroke and cancer risks quantified across very large populations.
Human biomarker / pharmacology
ProvenOvulation suppression directly demonstrable.
Animal
ProvenExtensive.
Cell / in vitro
ProvenReceptor pharmacology established.
Mechanistic plausibility
ProvenOvulation suppression and endometrial/cervical effects fully characterised.
The bottom line
What we know, what we think, what we don't know — and what would change our mind.
What We Know
Hormonal contraception works, and in TYPICAL use the differences between methods are enormous: about 7 in 100 pill users get pregnant each year, versus fewer than 1 in 100 using an implant or a coil. Combined methods raise the risk of blood clots — a real but small absolute increase — and are absolutely contraindicated in migraine with aura. And the combined pill substantially reduces the lifetime risk of ovarian and endometrial cancer, with protection lasting for decades after stopping.
What We Think
For most people wanting reliable contraception, a long-acting method is the better choice, and the reason is not that it is 'stronger' — it is that there is nothing to forget. The cancer picture is probably net favourable and is almost universally reported as though it were not. And the mood question deserves to be taken seriously rather than dismissed.
What We Don't Know
Whether hormonal contraception causes depression, and in whom. An association is consistently found in large cohorts, strongest in adolescents, but confounding is difficult to exclude and the absolute numbers are modest. We do not know how to predict who will be affected — which is the question a person actually wants answered.
Active Research
The mood question. Male hormonal contraception, which is closer than it has been. Non-hormonal alternatives. And better characterisation of who is at genuine VTE risk, so that the combined pill can be avoided in the few rather than feared by the many.
What Could Change Our Mind
A well-designed randomized trial demonstrating a causal effect on mood would move that claim from 'mixed' to 'supported' and should change prescribing in adolescents. Nothing on the horizon is likely to overturn the efficacy or the cancer findings — those are settled.
The biggest myth
“The pill is over 99% effective”
True with PERFECT use, and misleading as it is universally presented. In TYPICAL use — actual humans, who forget pills, get diarrhoea, travel across time zones and run out — roughly 7 in 100 pill users become pregnant each year. The implant, IUS and copper IUD fail in fewer than 1 in 100 in typical use, because there is nothing to remember. That roughly tenfold gap is the single most decision-relevant fact in contraception, and the '99%' figure on the packet is precisely what conceals it.
Ask BioSignal
Still have a question about hormonal contraception?
Answers are retrieved from this record and the rest of the knowledge graph — never generated.
Why people take hormonal contraception
Popularity is not evidence — but it is not stupid either. This explains the interest on its own terms.
Because almost everything people believe about hormonal contraception is either the wrong half of a true fact or a number that measures the wrong thing. 'Over 99% effective' measures perfect use, which nobody achieves. 'The pill causes cancer' reports the small increase and omits the large decrease. 'It causes weight gain' is untrue except for the one method where it is. And a question that takes five seconds — do you get aura with your migraines? — is the difference between a safe prescription and a doubled stroke risk, and it frequently goes unasked. This record exists to put the other half of each sentence back.
If you're here because…
Jump straight to the part of the evidence that answers your question.
Approval, safety and regulatory
What it is approved for, who should be careful, what remains unknown — and the limits of what this evidence can tell you.
Regulatory status
Approved. Multiple methods licensed for contraception; several also licensed for heavy menstrual bleeding
Availability
Prescription; some methods available without prescription in some jurisdictions
Sport (WADA)
Not a prohibited class (confirm at publication)
Known safety profile
Safe for the large majority of users. The risks are specific, identifiable in advance, and largely avoidable by choosing an appropriate method — which is why the assessment before prescribing is not a formality.
Common issues
- Irregular bleeding or spotting, particularly in the first months, and especially with progestogen-only methods
- Breast tenderness, nausea and headache in early use
- Mood change — reported by a minority, contested in the literature, and a legitimate reason to switch method
- Weight gain with the INJECTABLE (depo) specifically — a real effect, unlike with other methods
- Delayed return of fertility after the injectable (up to ~9–12 months)
Use caution if
- MIGRAINE WITH AURA — combined methods are ABSOLUTELY CONTRAINDICATED. Roughly doubled ischaemic stroke risk. Progestogen-only options are safe
- Smokers over 35 — combined methods contraindicated (cardiovascular risk)
- Personal or strong family history of venous thromboembolism, or known thrombophilia
- Uncontrolled hypertension
- Current or recent breast cancer
- Severe liver disease
- Breastfeeding in the early weeks — progestogen-only methods are preferred
- Interacting medications: enzyme-inducing drugs and, notably, ST JOHN'S WORT, which can reduce the effectiveness of hormonal contraception and cause it to fail
Long-term unknowns
Long-term use is extremely well characterised. The genuine residual uncertainty is the mood question, and the effects of very-long-duration LARC use, which is a newer pattern.
Limits of this evidence
The efficacy and vascular safety evidence is mature and reliable. The mood evidence is the exception: it is observational, susceptible to confounding, and cannot yet tell an individual whether she will be affected — which is precisely what she wants to know. BioSignal reports that uncertainty rather than resolving it in whichever direction is more comfortable.
Full regulatory and sport detail
- Regulatory approval
- Approved. Combined and progestogen-only pills, implants, intrauterine systems, injectables, patches and rings are licensed for contraception. The levonorgestrel IUS is additionally licensed for heavy menstrual bleeding.
- Approved indication
- Contraception; the LNG-IUS also for heavy menstrual bleeding.
- Sport (WADA)
- Not a WADA-prohibited class — confirm against the current list.
- Publication note
- Re-confirm contraindications, especially migraine with aura and VTE criteria, against current prescribing guidance at publication.
Demand, separated from evidence
Every claim people make about this, counted against what the evidence actually showed.
BioSignal evaluated 8 popular claims about hormonal contraception.
Here is where each one landed — including the claims of harm, where “not established” is reassuring rather than damning.
- Supported by evidence
- 1
- Mixed evidence
- 3
- Not established
- 4
Popularity is not evidence. This is simply a count of every claim BioSignal evaluated on this page, sorted by what the evidence actually showed — the full reasoning behind each verdict is in the Evidence Review below.
Supported by evidence
- The combined pill increases the risk of blood clots
Mixed evidence
- The pill is over 99% effective
- Hormonal contraception causes depression
- Hormonal contraception causes cancer
Not established
- Hormonal contraception causes weight gain
- The combined pill is safe if you get migraines with aura
- Hormonal contraception causes infertility
- You need to take a break from the pill
The evidence review
Every claim with the reasoning behind its verdict, the doses actually studied, where scientists agree and disagree, and the questions still open.
What people claim
Every popular claim, with BioSignal’s verdict and how confident we are in it. The verdicts are always visible; open any claim to read the evidence behind it.
Hormonal contraception causes weight gainNot establishedModerate confidence
For the pill, the implant and the IUS: not established. Reviews do not find a meaningful effect on body weight, and the belief is one of the commonest reasons people stop. There is ONE real exception, and it should not be buried: the injectable (depot medroxyprogesterone, 'the depo') IS associated with genuine weight gain. So the honest answer is 'no — except for the one where the answer is yes'.
Hormonal contraception causes depressionMixedLimited evidence
This deserves neither the dismissal nor the alarm it usually gets. Large cohort studies do find an association between hormonal contraception and subsequent diagnosis of depression, strongest in adolescents. But causality is genuinely contested, confounding is hard to exclude, and the absolute risk increase is modest — most users experience no mood effect at all. What this means practically: if your mood changed after starting, you are not imagining it and you should not be told you are. It is a good reason to change method, which is easy, and a poor reason to avoid contraception altogether.
The combined pill increases the risk of blood clotsSupportedHigh confidence
Yes — and the magnitude is worth stating precisely, because it is routinely both overstated and understated. Combined hormonal contraception raises the risk of venous thromboembolism roughly two- to four-fold. The absolute risk in a healthy young person remains LOW, and it is lower than the VTE risk of pregnancy itself, which is the comparison almost never offered. The risk is concentrated in the first year, and in smokers over 35, obesity, and inherited thrombophilia. Progestogen-only methods and the IUS do not carry this risk.
The combined pill is safe if you get migraines with auraNot establishedHigh confidence
NO. This is an ABSOLUTE CONTRAINDICATION, not a caution. In people who get migraine WITH AURA — visual disturbance, zigzag lines, blind spots or tingling before the headache — the combined pill roughly doubles the risk of ischaemic stroke, and every major guideline prohibits it. Migraine WITHOUT aura is a different matter and is generally compatible. The problem is that huge numbers of people have never been asked the question, and it is one question. If you get aura, you should not be on a combined method — progestogen-only options are safe.
Hormonal contraception causes cancerMixedHigh confidence
The truth is two-sided and only one side gets reported. The combined pill is associated with a SMALL increase in breast cancer risk while it is being used, which returns to baseline within about ten years of stopping. It is also associated with a SUBSTANTIAL REDUCTION in ovarian and endometrial cancer — a large effect that persists for DECADES after stopping and that grows with duration of use. Taken together the net effect on cancer is probably favourable. Reporting only the frightening half of a two-sided finding is not caution; it is a distortion, and it is the one people have absorbed.
Hormonal contraception causes infertilityNot establishedHigh confidence
It does not. Fertility returns rapidly after stopping the pill, the implant, or the IUS — most people ovulate within a cycle or two. There is one exception with a specific number: the injectable (depo) can delay return of fertility by up to around 9–12 months after the last injection, which is a reason to choose a different method if pregnancy is planned within a year. The persistent belief that the pill causes lasting infertility is false, and it causes people to avoid effective contraception for no reason.
You need to take a break from the pillNot establishedHigh confidence
There is no benefit to a 'break', and there is a clear harm: you can get pregnant during it. The idea that the body needs to 'reset' has no physiological basis. There is also no medical requirement to have a monthly bleed — the withdrawal bleed on the combined pill is an artefact of how the pill was originally designed to look natural, not a health need. Continuous use is a legitimate, evidence-supported option and is standard practice for endometriosis and heavy bleeding.
Doses used in human studies
What was actually given to participants in the research. These are descriptions of studies, not recommendations.
Anyone wanting the most reliable contraception
- Intervention
- Implant, levonorgestrel IUS, or copper IUD (LARC)
- Dose
- Fitted; lasts 3–10 years depending on device
- Duration
- Years
- Outcome
- Pregnancy prevention
- Notes
- TYPICAL-use failure under 1 in 100 per year — because there is nothing to remember.
Combined hormonal contraception
- Intervention
- Combined pill, patch, or vaginal ring
- Dose
- Daily / weekly / monthly per method
- Duration
- Ongoing
- Outcome
- Pregnancy prevention
- Notes
- TYPICAL-use failure ~7 in 100 per year. CONTRAINDICATED in migraine with aura.
People who cannot or should not use oestrogen
- Intervention
- Progestogen-only pill, implant, IUS, or injection
- Dose
- Per method
- Duration
- Ongoing
- Outcome
- Pregnancy prevention
- Notes
- No VTE excess. Suitable in migraine with aura, in smokers over 35, and while breastfeeding.
Heavy menstrual bleeding or endometriosis pain
- Intervention
- Levonorgestrel IUS, or continuous combined pill
- Dose
- Per method; continuous rather than cyclical
- Duration
- Ongoing
- Outcome
- Reduced bleeding / reduced pain
- Notes
- Prescribed here as TREATMENT, not merely contraception. There is no need for a monthly bleed.
Where scientists agree — and don’t
Agreed
- Long-acting methods are far more effective than the pill in typical use.
- Combined hormonal contraception raises VTE risk; progestogen-only methods do not.
- Migraine with aura is an absolute contraindication to combined methods.
- The combined pill substantially reduces ovarian and endometrial cancer risk, for decades.
- Fertility returns rapidly after stopping (except the injectable).
- There is no medical need for a monthly withdrawal bleed, and no benefit to a 'break'.
Debated
- Whether hormonal contraception causes depression, in whom, and by how much.
- The magnitude and clinical importance of the breast cancer association.
- Whether adolescents should be counselled differently about mood.
Unknown
- How to predict who will experience a mood effect — the question users actually want answered.
- The long-term effects of very-long-duration LARC use, which is a newer pattern of use.
What remains unknown
- Is the association between hormonal contraception and depression causal, and if so, in whom?
- Can the small group at genuine VTE risk be identified in advance, so the combined pill is avoided by the few rather than feared by the many?
- How should the net cancer effect — protective for ovary and endometrium, slightly adverse for breast — be communicated honestly?
Questions people actually ask
Which contraception is the most effective?
Long-acting reversible contraception — the implant, the hormonal coil (IUS) and the copper coil (IUD) — and the gap is much wider than most people realise. The pill is described as 'over 99% effective', which is true with PERFECT use and misleading in practice: in typical use, roughly 7 in 100 pill users become pregnant each year, because human beings forget pills, get ill, and travel. The implant and coils fail in fewer than 1 in 100, and the reason is not that the hormones are stronger. It is that there is nothing to remember. If reliability is what you want, that single fact should dominate the decision.
I get migraines. Can I take the pill?
It depends entirely on ONE question, and it is a question a great many people have never been asked: do you get AURA? Aura is a warning phase before the headache — flashing or zigzag lines, blind spots, tingling, or difficulty speaking. If you get migraine WITH aura, the COMBINED pill is an ABSOLUTE CONTRAINDICATION: it roughly doubles the risk of ischaemic stroke, and every major guideline prohibits it. This is not a caution to be weighed; it is a rule. Migraine WITHOUT aura is generally compatible with combined methods. And if you do get aura, you are not out of options at all — progestogen-only pills, the implant and the IUS are all safe and effective.
Does the pill cause depression?
This deserves a straight answer rather than the usual dismissal or the usual alarm. Large studies do find an association between hormonal contraception and later diagnosis of depression, and the signal is strongest in adolescents. Whether it is CAUSAL is genuinely contested, the absolute increase is modest, and most users experience no mood change at all. So: if your mood changed after you started, you are not making it up, and you should not be told that you are. It is a good reason to switch method — there are many, and they behave differently — and a poor reason to abandon contraception. If you feel persistently low, that is worth raising properly, not enduring.
Does hormonal contraception cause cancer?
The honest answer has two halves, and you have almost certainly only been told one. The combined pill is associated with a SMALL increase in breast cancer risk while it is being taken, which fades back to baseline within about a decade of stopping. It is also associated with a SUBSTANTIAL REDUCTION in ovarian cancer and endometrial cancer — a large effect, which increases the longer you use it, and which persists for DECADES afterwards. On balance the overall cancer effect is probably favourable. The reason you have only heard the first half is that it is the frightening half, and frightening halves travel further.
Will it affect my fertility later?
No. Fertility returns quickly after stopping the pill, the implant or the coil — most people ovulate within a cycle or two, and there is no lasting effect however long you used it. The persistent belief that the pill causes infertility is false, and it leads people to avoid effective contraception for no reason. There is one specific exception worth knowing: the INJECTION (depo) can delay the return of fertility for up to around nine to twelve months after the last dose, so if you are hoping to conceive within a year, it is the wrong method to choose.
Do I need a break from the pill? Do I need a monthly bleed?
No to both, and the first one is actively risky. There is no physiological 'reset' that a break provides — the only reliable effect of a break is that you can get pregnant during it. And the monthly bleed on the combined pill is not a period and is not a health requirement: it is a withdrawal bleed, and it exists because the pill was designed in the 1950s to LOOK like a natural cycle for reasons of acceptability, not medicine. Taking the combined pill continuously, without a break, is a legitimate and evidence-supported option — and it is standard treatment for endometriosis and heavy bleeding.
Practical takeaways
- TYPICAL use is the only number that matters: ~7 in 100 pill users get pregnant each year; under 1 in 100 with an implant or coil.
- MIGRAINE WITH AURA = NO COMBINED PILL. Absolute contraindication, roughly doubled stroke risk. Progestogen-only methods are safe.
- The cancer story is two-sided: a small breast cancer increase while using, and a LARGE, decades-long reduction in ovarian and endometrial cancer.
- It does not cause infertility, and it does not cause weight gain — with one honest exception each: the depo delays fertility, and the depo does cause weight gain.
- You do not need a monthly bleed, and you do not need a 'break'. Both ideas are artefacts, and the 'break' gets people pregnant.
How it works
The mechanism comes last on purpose. A compelling explanation of how something might work is the easiest part of the story to tell, and the part most likely to outlive the evidence for it.
Well characterised. Combined methods suppress ovulation; progestogen-only methods thicken cervical mucus, thin the endometrium and often suppress ovulation; the copper IUD is non-hormonal and spermicidal.
How we found out
The Withdrawal Bleed
The combined pill was designed with a monthly bleed to make it resemble a natural cycle — a decision made for social acceptability, not for health. Decades later, people still believe the bleed is medically necessary. It is not.
The VTE Signal
Clotting risk with combined methods was identified early and quantified. Formulations were reduced in oestrogen dose in response, and the absolute risk — still lower than that of pregnancy — is now well characterised.
The Cancer Findings
Long-running cohorts established both halves of the cancer picture: a small breast cancer increase during use, and a large, durable reduction in ovarian and endometrial cancer. Only one half entered public consciousness.
The LARC Shift
Recognition that TYPICAL-use failure rates — not perfect-use rates — are what matter moved guidelines to recommend long-acting methods first. The pill's '99%' had been measuring the wrong thing for decades.
The Mood Question
Large registry studies reported an association with subsequent depression, strongest in adolescents, reopening a question that had long been dismissed. It remains genuinely unresolved.
References
Verified sources. BioSignal does not print a citation it has not checked.
References for this record are being verified and will be published with the next review. BioSignal does not print citations it has not checked.
Version history
Version 1.0
Initial record. Published as a Signal Record rather than a Condition because contraception is not a disease — following the Antidepressants and Anticoagulants precedent for drug classes. Calibration: Established maturity, HIGH confidence. Three facts carried as the record's purpose: typical-use efficacy (not the '99%' on the packet), the absolute contraindication in migraine with aura, and the untold half of the cancer story. The mood claim is graded MIXED at limited confidence deliberately — dismissing it insults people who experienced something real, and amplifying it overstates a contested signal. Review cadence: Annually.
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