Natural birth control is an option for people who cannot or do not want to use hormonal birth control to prevent pregnancy. There are various natural birth control methods, but some of these are not as effective as hormonal contraception.

Abstinence. Doesn’t work as birth control in case of forced coitus.

The withdrawal method (the man pulls out before ejaculation). Unreliable, because not everyone can control themselves to such an extent, but also because a certain amount of sperm can be present in the pre-ejaculate also before ejaculation. But does work for many people.

Calendar method. The woman counts the days in her menstrual cycle to know the period when she should be fertile or not. Unreliable, because ovulation can happen irregularly.

Fertility awareness method. The woman monitors the symptoms of ovulation in her body (the viscosity of vaginal secretions, basal temperature, mood swings, etc.) to avoid that period. More reliable than the calendar method because the body is more strictly monitored, but it’s still prone to failure, not least because some resilient sperm cells can survive up to two weeks.

Avoiding vaginal penetration. A solid method, and has been used by humans for millennia, but it’s also not foolproof, as certain positions can enable sperm leaks from the anus to the vulva, and I have personally been in a situation when a man smeared his ejaculate over me and then decided to finger me with the same hand. I was saved by an emergency contraception pill.

Depending on your definition of “natural”, barrier methods (condoms, diaphragms, sponges) can also be counted as natural because they don’t affect the body in any way and are merely an obstacle to sperm flow. Of these, the condom is the most effective, if used correctly.