Natural methods work on the principle of avoiding chances of ovum and sperms meeting which are as follow :

$(i)$ Periodic abstinence : It is one such method in which the couples avoid or abstain from coitus from day $10$ to $17 $ of the menstrual cycle when ovulation could be expected. As chances of fertilization are very high during this period. It is called fertile period. Therefore abstaining from coitus during this period conception could be prevented.

$(ii)$ Coitus interruptus: In this method male partner withdraws his penis from the vagina just before ejaculation so as to avoid insemination.

$(iii)$ Lactational amenorrhea : This method is based on the fact that ovulation and therefore the cycle do not occur during the period of intense lactation following parturition. Therefore as long as the mother breast feeds the child fully, the chances of conception are almost nil.This method has been reported to be effective only upto a maximum period of six months following parturition.

As no medicines or devices are used in these methods, side effects are almost nil. Chances of failure though of this method are also high.