7. Castor oil - Statistically speaking it only works on 57% of women and causes lovely things like diarrhoea and sometimes, vomiting. The theory is that the cramps in the bowel set off contractions. Opinion is still out on whether castor oil causes babies to pass meconium in the womb but a) most women using castor oil are overdue and b) babies that are overdue are more likely to pass meconium, so you do the maths! WARNING : Please read the linked article before attempting and make sure you're fully informed on the safe methods to induce with castor oil.