Only barrier contraception, such as condoms, prevent STIs from being passed on.
Any sexual contact without a condom may pass on STIs.
Some things make the injection less effective - that means it doesn't work properly!
Small plastic T-shaped device which releases the hormone progestogen. It is fitted into the womb by a doctor or nurse.
Stops sperm meeting an egg or may stop an egg implanting in the womb.
The IUS is 99% effective when used correctly.