Plan B is recommended for use within 72 hours of unprotected sex, but the sooner you take it, the better, as it becomes less effective over time. Another consideration to take into account is your weight, Dr. Haynes explains, as Plan B may not work for those who weigh more than 165 pounds. If that’s the case for you, IUDs or Ella might be better options. “Ulipristal acetate (Ella) is another oral emergency contraceptive available,” says Dr. Haynes. “It is slightly more effective than Plan B, with less than 1-3% pregnancy rates after use, though it requires a prescription and is less widely available.”