Intrauterine devices (IUD) are often called copper Ts, but they may also be of another variety known as levonorgestrel. They are one of the older contraceptive devices that are in use. They are inserted into the uterus of the female individual and they are considered to be one of the more effective types of reversible birth control available. As with all contraceptive devices, this form is also not 100 per cent successful. Both the varieties of the IUD contraceptive have a failure probability of around 0.5%. This does however mean that in the vast majority of cases they are successful, and hence they are the most popular contraceptive device in the world, with almost 200 million users globally, at last count. The IUD contraceptive is so popular as it has a variety of advantages. It can be used effectively in adolescents and also on those who have not previously been pregnant. The device can also be used right after an abortion and it also does not affect the fertility of the user after its removal. In the US, the largest user of IUD devices, there are two types available. These are Paraguard and mirena varieties. Within these two options there are again several sub varieties. This great choice available, make the IUD device the most sought after contraceptive device in the market.