What are the different methods of human contraception, and how do they work to prevent pregnancy?

There are several methods of human contraception, each working in different ways to prevent pregnancy. Here are some of the most common methods:

1. Barrier Methods: These include condoms, diaphragms, and cervical caps. They work by physically preventing sperm from reaching the egg. Condoms have the added benefit of protecting against sexually transmitted infections.

2. Hormonal Methods: These include birth control pills, patches, injections, vaginal rings, and implants. They work by regulating a woman's hormones to prevent ovulation - if no egg is released, pregnancy can't occur. Some also thicken cervical mucus to make it harder for sperm to reach the egg.

3. Intrauterine Devices (IUDs): These are small devices inserted into the uterus. There are two types - copper and hormonal. The copper IUD releases copper into the uterus, which is toxic to sperm. The hormonal IUD releases progestin, which thickens cervical mucus to prevent sperm from reaching the egg and also sometimes stops ovulation.

4. Emergency Contraception: This includes pills like Plan B or Ella, or the copper IUD. These methods can be used after unprotected sex to prevent pregnancy. Plan B and Ella work by delaying ovulation, while the copper IUD can prevent the sperm from fertilizing the egg.

5. Natural Methods: These include fertility awareness methods, where a woman tracks her menstrual cycle and avoids sex on her most fertile days. This method requires a good understanding of the menstrual cycle and is less reliable than other methods.

6. Sterilization: This includes vasectomies for men and tubal ligation for women, which are surgical procedures that provide permanent contraception. A vasectomy involves cutting or blocking the tubes that carry sperm, while tubal ligation involves cutting or blocking the fallopian tubes so an egg cannot reach the uterus.

Each method has its own effectiveness rate and side effects, so it's important to talk to a healthcare provider to decide which method is best for you.