The implant and the injection

An implant is a small rod placed under the skin of your arm. The contraceptive injection provides progestogen in a different way. Both prevent pregnancy by stopping the ovaries releasing eggs, but their duration and the return of fertility after use are different.

How long they work

The NHS now says the implant works for 5 years. In the US, ACOG confirms that Nexplanon is approved for up to 5 years. Advice has changed recently: ACOG describes the updated US approval.

Check the name of your implant and your replacement plan with the clinic that fitted it, especially if you have an older card or leaflet. You can have the implant removed before then if you no longer want it. A trained doctor or nurse can do this.

The NHS gives an injection duration of 8 to 13 weeks, depending on the type. ACOG’s US guidance describes depot medroxyprogesterone acetate, or DMPA, which protects against pregnancy for 13 weeks. Use the appointment and product instructions from your own service; ask them to confirm when your next injection is due rather than calculating it yourself.

Timing matters for effectiveness. NHS inform says an implant is more than 99% effective. The NHS describes the injection as more than 99% effective with correct use, but less effective if an injection is late. Ask the clinic for advice if you are unsure about your next appointment.

Bleeding can change with either method

With an implant, bleeding may stop, become infrequent or last longer. Bleeding patterns often remain irregular. If the bleeding is a problem, speak to your GP, nurse or sexual health service.

With the injection, periods may stop, become irregular or last longer. Weight gain and discomfort, a small lump or a scar at the injection site are also listed side effects. Speak to a doctor or nurse if any of these are a problem for you.

At a review, describe how bleeding affects your day. It might interrupt a work shift, or you might simply dislike the pattern. Either is a reason to ask about another option.

Bone health and other risks of the injection

The NHS says using the injection for more than 1 year can weaken bones. ACOG describes bone loss during use and says at least some, and sometimes all, of the lost bone is regained after injections stop. Bring any bone-health concerns to your prescriber before deciding on the method.

Your clinician will also need to review your medical history when discussing the injection. The NHS notes an increased blood-clot risk and says a previous clot or a condition such as thrombophilia may make a different method preferable. It also describes a very small increase in breast and cervical cancer risk.

Current NHS information links the injection with a small increased risk of meningioma, a type of non-cancerous brain tumour. Ask your clinician how these risks relate to your circumstances. Do not change a prescribed contraceptive plan without discussing the alternatives.

How soon fertility returns

After implant removal, the NHS says your chance of pregnancy returns to its previous level straight away. After stopping the injection, fertility can take up to 1 year to return to previous levels. If pregnancy might be something you want soon, discuss that difference before choosing.

ACOG describes a different outcome: an average of 10 months to become pregnant after stopping the injection, with some people taking longer. Time to pregnancy and return of fertility measure different things. Neither figure gives you a personal deadline.

When to get help

Call 999 now (UK) or 911 (US), or your local emergency number, for severe breathlessness, chest pain or collapse. Do not wait for leg symptoms.

Contact an urgent GP service or NHS 111 today (UK), or your doctor or urgent care service (US and elsewhere), for new leg pain and swelling, particularly on one side.

Contact your fitting clinic, an urgent GP service or NHS 111 today (UK), or your doctor or urgent care service (US and elsewhere), if you can no longer feel the implant, think it has moved, or the site becomes painful, hot and swollen.

Book a review with those services if bleeding or other side effects bother you. Neither method protects against STIs; condoms can provide protection alongside your chosen contraception.