A study of more than two million women found a real increase in risk. It also found the absolute numbers are small — and one method with no increase at all. Both halves belong in the same sentence.
The study is large and serious. Published in The BMJ on 12 February 2025, it followed 2,025,691 women aged 15–49 in Denmark between 1996 and 2021, over 22,209,697 person-years, recording 4,730 ischaemic strokes and 2,072 heart attacks.
The relative risk roughly doubled — and the absolute risk stayed low. Combined oral contraceptives were associated with a 2-fold increase in both stroke and heart attack. In absolute terms that’s about 21 extra strokes and 10 extra heart attacks per 100,000 person-years — roughly one extra stroke per 4,760 women per year and one extra heart attack per 10,000 women per year.
The levonorgestrel IUD showed no increased risk at all. And nothing here is a reason to stop contraception without talking to a doctor first. 🩺
- What the study actually was
- The numbers, method by method
- Relative vs absolute risk
- The method with no increased risk
- Why not to stop suddenly
- The comparison that’s usually missing
- Who should have a closer conversation
- Blood pressure: the checkpoint that matters
- Warning signs to act on immediately
- What this study can’t tell you
- How to have the conversation
- Frequently asked questions
- Your checklist
What the study actually was
This is an unusually strong piece of evidence for a question that’s normally hard to study, and the design explains why.
| Element | Detail |
|---|---|
| Published | The BMJ, 12 February 2025 |
| Design | Real-world, nationwide, prospective cohort study |
| Population | All women aged 15–49 living in Denmark, 1996–2021 |
| Number of women | 2,025,691 |
| Follow-up | 22,209,697 person-years |
| Ischaemic strokes | 4,730 |
| Heart attacks | 2,072 |
Two features make this stronger than most: it covered an entire national population rather than a sample, which removes much of the selection bias that plagues this field, and it ran for 25 years, so it captured genuinely rare events in numbers large enough to analyse.
The numbers, method by method
The findings varied substantially by method, which is the most practically useful part of the whole study.
| Method | Stroke | Heart attack | Extra events per 100,000 person-years |
|---|---|---|---|
| Combined oral pill | 2.0× (1.9–2.2) | 2.0× (1.7–2.2) | 21 strokes, 10 heart attacks |
| Vaginal ring | 2.4× (1.5–3.7) | 3.8× (2.0–7.3) | 28 strokes, 41 heart attacks |
| Patch | 3.4× (1.3–9.1) | No heart attacks observed | Few absolute events — small numbers using it |
| Progestogen-only pill | 1.6× (1.3–2.0) | 1.5× (1.1–2.1) | 15 strokes, 4 heart attacks |
| Levonorgestrel IUD | 1.1× (1.0–1.3) | 1.1× (0.9–1.3) | No increased risk |
Look carefully at the patch row. A 3.4-fold increase sounds like the most alarming number in the table — but the confidence interval runs from 1.3 to 9.1, which is enormously wide, and reflects a small number of users. A wide confidence interval means the true figure is poorly pinned down. The combined pill’s interval of 1.9–2.2 is narrow, which is why that estimate is the most trustworthy one here.
Relative vs absolute risk
This is the distinction that decides whether this study is frightening or manageable, and headlines almost always report only the first half.
“Doubles your risk” is a relative statement. It tells you nothing about the starting point. Doubling a very small number produces a slightly less small number.
The absolute figures for the combined pill:
- 21 extra strokes per 100,000 person-years — about one additional stroke per 4,760 women per year.
- 10 extra heart attacks per 100,000 person-years — about one additional heart attack per 10,000 women per year.
“Combined oral contraceptives double the risk of stroke and heart attack” and “if 4,760 women take the combined pill for a year, roughly one additional stroke occurs among them” describe exactly the same finding. The first is accurate and frightening; the second is accurate and proportionate. Whenever you read a health headline reporting a doubled or tripled risk, the useful question is always “of what baseline?” — and if the article doesn’t say, it hasn’t given you enough to make a decision.
The study’s own authors framed it that way: although absolute risks were low, clinicians should include the potential risk of arterial thrombosis when weighing the benefits and risks of prescribing hormonal contraception. That’s a call for better-informed conversations, not for anyone to stop.
The method with no increased risk
The single most actionable finding is the one that didn’t make the headlines.
The levonorgestrel-releasing intrauterine device was the only method not associated with an increased risk of arterial thrombosis — rate ratios of 1.1 for stroke (1.0–1.3) and 1.1 for heart attack (0.9–1.3), both effectively indistinguishable from no increase.
That makes sense mechanistically: it acts largely locally rather than delivering hormone systemically at the levels the pill, ring and patch do.
If cardiovascular risk is your specific concern, this is the conversation to have with your doctor. Not “should I stop contraception,” but “given my risk profile, is a different method better for me?” That’s a question with a good answer, and stopping altogether is not it.
Why not to stop suddenly
Stopping hormonal contraception without an alternative in place risks unintended pregnancy — and pregnancy itself carries a substantially higher cardiovascular risk than any of the methods in this study. Pregnancy increases clotting risk, blood volume and cardiac workload, and the postpartum period carries elevated risk too. Swapping a small increase for a larger one is a bad trade made in a moment of alarm.
Keep taking your contraception and book an appointment. Bring the questions in this article. If a change makes sense for you, your doctor will arrange it in a way that doesn’t leave you unprotected in between.
The comparison that’s usually missing
A study like this reports the risk of a medication. It cannot report the risk of the alternative, because that isn’t what it measured — and that omission does a lot of damage when the finding reaches the public.
Contraception is not compared against nothing happening. For someone who is sexually active and doesn’t want to be pregnant, it’s compared against a meaningful probability of pregnancy — which carries its own cardiovascular risks, along with everything else pregnancy involves for someone who didn’t choose it.
The other missing side of the ledger: combined hormonal contraception also has documented benefits beyond preventing pregnancy, including for heavy or painful periods, and reductions in the risk of some cancers. Those don’t disappear because a new risk figure was published.
A risk figure in isolation isn’t a decision. A decision needs the alternatives on the table too — which is precisely what a doctor’s appointment is for and a headline is not.
Who should have a closer conversation
The finding matters more for some people than others. Bring it up sooner rather than at your next routine review if you:
- Have high blood pressure, or have had raised readings.
- Smoke — the interaction between smoking and combined hormonal contraception is well established, and matters increasingly with age.
- Get migraine with aura. This is a specific and important one: it changes the safety assessment for combined hormonal contraception and is worth raising explicitly.
- Have diabetes, particularly with any complications.
- Are over 35, especially in combination with any of the above.
- Have a personal or strong family history of stroke, heart attack or blood clots.
- Have raised cholesterol or other cardiovascular risk factors.
- Use the ring or patch and have other risk factors — these showed higher rate ratios than the pill.
Blood pressure: the checkpoint that matters
Of all the risk factors above, blood pressure is the one that is both strongly relevant and completely silent until measured.
Combined hormonal contraception can raise blood pressure in some people, and uncontrolled hypertension changes the safety calculation significantly. It’s why any decent contraception review includes a blood pressure check — and why skipping those reviews is a genuine risk rather than an administrative inconvenience.
Automatic Blood Pressure Monitor
Blood pressure is a major factor in this risk assessment, produces no symptoms, and is the easiest thing on the list to check
If this study has made you want to do something constructive, this is it. Blood pressure is directly relevant to the cardiovascular risk of combined hormonal contraception, it can be affected by it, and it gives no warning at all until it’s measured. A home monitor lets you bring your doctor a week of real readings rather than one anxious measurement in a clinic. Choose an upper-arm cuff rather than a wrist device, check the cuff size fits, sit quietly for five minutes first with feet flat and arm supported, and measure at the same time each day for a week before drawing any conclusion. Bring the log to your appointment. This supports your medical care — it does not replace a contraception review, and it is not a reason to change or stop anything on your own.
- Upper-arm cuffs are more reliable than wrist models
- Check the cuff size fits — the wrong size gives wrong numbers
- Measure at the same time daily and write it down
- Never stop or change contraception based on home readings
- A single high reading means repeat it, not panic
Warning signs to act on immediately
Stroke. Remember FAST: Face drooping on one side, Arm weakness, Speech difficulty, Time to call emergency services. Also: sudden severe headache unlike any before, sudden loss or blurring of vision, sudden confusion, sudden numbness on one side.
Heart attack. Chest pain, pressure or tightness; pain spreading to the arm, jaw, neck or back; shortness of breath; nausea; sweating; light-headedness. Symptoms in women can be less typical — breathlessness, unusual fatigue, nausea or back and jaw pain without dramatic chest pain. Take them seriously.
Blood clot. Pain, swelling, warmth or redness in one leg; sudden breathlessness or chest pain worse on breathing in; coughing blood.
These apply to everyone, not only people using hormonal contraception. Call emergency services immediately — do not drive yourself and do not wait to see if it passes.
What this study can’t tell you
Being fair to the evidence means naming its limits as clearly as its findings:
- It’s observational, not randomised. It shows association. Careful cohort design reduces confounding but cannot eliminate it entirely.
- It’s one country. Denmark’s population and prescribing patterns may not match yours.
- Some estimates rest on small numbers. The patch’s wide confidence interval is the clearest example.
- It reports population averages, not your personal risk — which depends on your age, blood pressure, smoking status, migraine history and family history.
- It doesn’t weigh benefits. Contraceptive efficacy, cycle control and other documented benefits weren’t the subject.
- It can’t compare against pregnancy risk, which is the real-world alternative for many people.
How to have the conversation
Bring these to your appointment, and keep taking your contraception until you’ve had it:
- “Given my blood pressure, smoking status, age and family history, what’s my personal risk profile?”
- “I get migraine with aura” — say this explicitly if it applies; it specifically affects the assessment.
- “Would the levonorgestrel IUD be a reasonable option for me?” It was the only method without increased arterial risk.
- “Should I be on the ring or patch given my risk factors?” Both showed higher rate ratios than the pill.
- “How often should my blood pressure be checked?”
- “What warning signs should I act on?”
- “If I change method, how do we avoid a gap in cover?”
Frequently asked questions
Should I stop taking my birth control pill?
Not because of this study, and not without speaking to a doctor. Stopping without an alternative in place risks unintended pregnancy — and pregnancy carries a substantially higher cardiovascular risk than any method in this study, along with everything else it involves for someone who didn’t choose it. The study’s authors called for clinicians to include arterial thrombosis risk in their prescribing assessment; that’s a request for better-informed conversations, not for anyone to stop. Keep taking it and book an appointment.
How much does the risk actually increase?
For combined oral contraceptives, the rate roughly doubled — 2.0× for both ischaemic stroke and heart attack. In absolute terms that’s 21 extra strokes and 10 extra heart attacks per 100,000 person-years: about one additional stroke per 4,760 women per year, and one additional heart attack per 10,000 women per year. Both descriptions are of the same finding. “Doubled” is accurate; so is “roughly one extra stroke among 4,760 women in a year.” When you read any doubled-risk headline, the question that matters is always “doubled from what?”
Which method had the lowest risk?
The levonorgestrel-releasing IUD was the only method not associated with any increased risk of arterial thrombosis — rate ratios of 1.1 for stroke (1.0–1.3) and 1.1 for heart attack (0.9–1.3), both effectively no increase. That fits its mechanism, since it acts largely locally rather than delivering hormone systemically. If cardiovascular risk is your particular concern, this is worth raising specifically with your doctor as an alternative rather than considering stopping contraception altogether.
Are the ring and patch riskier than the pill?
They showed higher rate ratios in this study — the vaginal ring 2.4× for stroke and 3.8× for heart attack, and the patch 3.4× for stroke with no heart attacks observed. But read those with care: the patch’s confidence interval ran from 1.3 to 9.1, which is very wide and reflects small numbers of users, so the true figure is poorly pinned down. The combined pill’s interval of 1.9–2.2 is narrow and therefore the most reliable estimate in the table. If you use the ring or patch and have other risk factors, that’s worth discussing.
Who is most affected by this finding?
People with existing cardiovascular risk factors: high blood pressure, smoking, diabetes, raised cholesterol, being over 35 (especially combined with the others), and a personal or strong family history of stroke, heart attack or clots. Migraine with aura deserves a specific mention — it changes the safety assessment for combined hormonal contraception and should be raised explicitly with your prescriber if it applies to you.
What symptoms should I go to hospital for?
For stroke, remember FAST: face drooping, arm weakness, speech difficulty, time to call emergency services — plus sudden severe headache, sudden vision loss, sudden confusion or one-sided numbness. For heart attack: chest pain or pressure, pain spreading to arm, jaw, neck or back, breathlessness, nausea, sweating — and note that symptoms in women can be less typical, including unusual fatigue or nausea without dramatic chest pain. For a clot: pain, swelling or redness in one leg, sudden breathlessness, or chest pain worse on breathing in. Call emergency services immediately; don’t drive yourself and don’t wait.
Your checklist
- Don’t stop your contraception because of a headline
- Know the relative figure: combined pill ≈ 2× for stroke and heart attack
- Know the absolute figure: ~1 extra stroke per 4,760 women per year
- The levonorgestrel IUD showed no increased risk
- Ring and patch showed higher rate ratios — worth discussing
- Treat wide confidence intervals as uncertain estimates
- Mention migraine with aura explicitly to your prescriber
- Get your blood pressure checked and keep a log
- Raise smoking, diabetes, age over 35, family history
- Remember pregnancy carries higher cardiovascular risk than these methods
- Learn FAST and the atypical heart attack symptoms in women
- Call emergency services for any warning sign — don’t wait
- Change methods with your doctor, without a gap in cover
Medical disclaimer. This article is general information and is not medical advice. Do not stop, change or start any contraceptive method based on this article — speak to your doctor, who can assess your individual risk factors and arrange any change without leaving you unprotected. Stopping contraception without an alternative risks unintended pregnancy, which carries its own substantial cardiovascular and other risks. Call emergency services immediately for any sign of stroke, heart attack or blood clot — do not drive yourself and do not wait to see whether symptoms pass.
Affiliate disclosure. Some links on this page are affiliate links. As an Amazon Associate we earn from qualifying purchases. The item recommended here is a measuring device that supports a medical conversation; it is not a treatment and not a substitute for one.
