The implant and the injection

An implant is a small rod placed under the skin of your arm. The contraceptive injection gives you progestogen in a different way. Both prevent pregnancy by stopping the ovaries from releasing eggs. They differ in how long they last and how soon fertility comes back afterwards.

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. This advice changed recently, and ACOG describes the new US approval.

Check the name of your implant and when it should be replaced with the clinic that fitted it. This matters most if you have an older card or leaflet. You can have the implant taken out sooner if you no longer want it. A trained doctor or nurse can do this.

The NHS says an injection lasts 8 to 13 weeks, depending on the type. ACOG’s US guidance describes depot medroxyprogesterone acetate (DMPA), which protects against pregnancy for 13 weeks. Follow the appointments and product instructions from your own service. Ask them to confirm when your next injection is due rather than working it out yourself.

Timing affects how well they work. NHS inform says an implant is more than 99% effective. The NHS says the injection is more than 99% effective with correct use, but less effective if an injection is late. Ask the clinic if you’re not sure when your next appointment is.

Bleeding can change with either method

With an implant, bleeding may stop, come less often or last longer. It often stays irregular. If the bleeding is a problem, talk to your GP, nurse or sexual health service.

With the injection, periods may stop, become irregular or last longer. Other listed side effects are weight gain, and discomfort, a small lump or a scar where the injection went in. Talk to a doctor or nurse if any of these bother you.

At a check-up, say how bleeding affects your day. It might disrupt a work shift, or you might just dislike the pattern. Either is a good 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 while you use it. It says at least some, and sometimes all, of the lost bone comes back after you stop. If you’re worried about your bones, talk to your prescriber before you decide.

Your clinician will also need to go through your medical history before you start the injection. The NHS notes a higher risk of blood clots. It says a past clot, or a condition such as thrombophilia (blood that clots too easily), may mean another method is better. It also describes a very small rise in the risk of breast and cervical cancer.

Current NHS information links the injection with a small rise in the risk of meningioma, a type of brain tumour that is not cancer. Ask your clinician how these risks apply to you. Don’t change a prescribed contraception plan without talking through the other options.

How soon fertility returns

The NHS says that once an implant is taken out, your chance of getting pregnant goes straight back to what it was. After you stop the injection, fertility can take up to 1 year to return to what it was. If you might want to get pregnant soon, talk about this difference before choosing.

ACOG gives a different measure: on average it takes 10 months to get pregnant after stopping the injection, and some people take longer. Time to get pregnant and the return of fertility measure different things. Neither figure is 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, especially 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 area becomes painful, hot and swollen.

Book a check-up with those services if bleeding or other side effects bother you. Neither method protects against STIs. You can use condoms as well as your chosen contraception for that.