Two effective contraceptive methods to control the size of human population are hormonal contraception and barrier methods. Hormonal contraception involves the use of hormones to prevent pregnancy by suppressing ovulation. This can be done through oral contraceptives, injections, implants, or vaginal rings. Barrier methods involve the use of physical barriers, such as condoms and diaphragms, to prevent sperm from entering the uterus. Both methods are highly effective in preventing pregnancy and help reduce the size of the human population.