Mirena is approved for use up to five years in the US, though studies support its efficacy for up to seven years.[32] Skyla uses the same mechanism of action, but is smaller and releases a lower dose of levonorgestrel, and is only approved for up to three years. Liletta is more similar to Mirena in both shape and dose of levonorgestrel released; it has currently been approved for usage up to three years.[33]