左炔诺孕酮是一种用于快速避孕的短效药物。它可以抑制排卵并阻止孕卵着床，同时使宫颈黏液浓度增大，阻止精子前进。代表商品名称有“毓婷”、“安婷”等。

服用左炔诺孕酮可能会造成轻微的呕吐、恶心。可能会造成女性下次月经提前或延期。 仍然有很多临床症状表明，左炔诺孕酮和子宫外孕有关。

Levonorgestrel is a manufactured hormone used in a number of birth control methods. In pill form, sold under the brand name Plan B among others, it is useful within 120 hours as emergency birth control. It becomes less effective the longer after sex and only works before pregnancy has occurred. It is also combined with an estrogen to make combined oral birth control pill. Within an IUD, sold as Mirena among others, it is effective for long term prevention of pregnancy. An implantable form of levonorgestrel is also available in some countries.