Start Here: Your Two Options and How Fast You Need to Move
Emergency contraception is a birth control measure used after unprotected sex to reduce the risk of pregnancy (Wikipedia). The NHS frames the same idea plainly: it can stop you getting pregnant after unprotected sex, meaning sex without contraception or when contraception might have failed (NHS). If you are reading this because something went wrong and you are counting hours, the two options you can name right now are the emergency contraceptive pill and the copper IUD.
| Option | What it is | Where it fits |
|---|---|---|
| Emergency contraceptive pill | A medicine taken after unprotected sex | The option most people ask for first |
| Copper IUD | An intrauterine device placed by a clinician | Usually used as a primary contraceptive method, and sometimes used as emergency contraception (Wikipedia) |
| Either route | Free from NHS sexual health clinics and GP surgeries | Cost should not be the reason you delay (NHS) |
The table is a starting map, not a ranking. The choice between these two turns on timing and on how effective each method is, and those are the next two decisions.
The Time Limits: Hours for the Pill, Days for the IUD
The outer limit is the same for both routes: you need to use emergency contraception within 3 to 5 days of having unprotected sex (NHS). Within that window, speed matters. The sooner you use emergency contraception, the more effective it usually is (NHS).
Safety and evidence boundary: The 3-to-5-day outer limit is the figure the NHS publishes, and it applies to emergency contraception as a category. The sooner you act within that window, the better it usually works (NHS). If you are past the window or unsure where you fall in it, contact a sexual health clinic or GP rather than waiting to see what happens.
Which Option Is Most Effective
The IUD is the most effective type of emergency contraception (NHS). Wikipedia’s entry agrees, describing IUDs as sometimes used as the most effective form of emergency contraception (Wikipedia). If effectiveness is your deciding factor and an IUD is available to you in time, that is the option the evidence points to.
| Option | Effectiveness signal | Practical note |
|---|---|---|
| IUD | Most effective type of emergency contraception (NHS) | Requires a clinician to place it |
| Emergency contraceptive pill | Effective, and more so the sooner it is taken (NHS) | The more commonly used route |
| Both | Free from NHS sexual health clinics and GP surgeries (NHS) | Ask which is available when you contact a service |
The effectiveness advantage of the IUD does not make it automatic. Wikipedia notes that use of IUDs for emergency contraception is relatively rare (Wikipedia), so availability and same-day access can shape what you actually get. If an IUD cannot be arranged quickly, the pill remains a real option, and acting sooner rather than later is what protects its effectiveness.
The Weight Caveat
Effectiveness is not only about hours. Body weight changes how well emergency contraception works, and heavier body weight is associated with reduced effectiveness. That caveat belongs in your decision alongside timing, because it can shift the balance toward the IUD, which is the most effective type (NHS).
If your weight is a concern, raise it directly when you contact a service. Ask which method is likely to work best for you given your weight and how long it has been since the unprotected sex. That conversation is the practical way to apply the caveat to your own situation rather than guessing.
What to Expect: Side Effects
Emergency contraception is a birth control measure taken after sex to reduce pregnancy risk (Wikipedia), and like any medication or procedure it can come with side effects. The specific side-effect profile differs between the pill and the IUD, so ask the clinician or pharmacist what to expect from the method you are given.
Knowing what to expect helps you tell a normal reaction from something that needs attention. If a symptom worries you after treatment, contact the service that provided it or a sexual health clinic rather than waiting.
Follow-Up: When to Test
Emergency contraception lowers the risk of pregnancy; it does not confirm that you are not pregnant. The practical follow-up is a pregnancy test, and the timing should be confirmed with the service that gave you emergency contraception, since it depends on which method you used and where you are in your cycle.
If your period is late, unusual, or lighter than normal after using emergency contraception, take a pregnancy test and speak to a clinician. Do not assume the method worked simply because you took it in time.
Where to Go and When to Stop
Emergency contraception is free from NHS sexual health clinics and GP surgeries (NHS), so cost is not a reason to wait. Contact a sexual health clinic or GP as soon as you can, state how many hours or days it has been since the unprotected sex, and ask which methods they can offer you that day.
That is the stop boundary: once you have named your options, matched them to the time window, weighed effectiveness and the weight caveat, and booked or attended a service, you have what you need to act. The remaining step is the appointment itself.