Ex-lax generally produces a bowel movement in six to 12 hours, according to the product's website. However, drugs affect people in different ways; a person's size, age and drug sensitivity determine how and when ex-lax works.
Ex-lax package instructions indicate that adults and children ages 12 and older should take two pills once or twice a day, and children between ages six and 12 should take one pill once or twice daily. If a dose is missed, take another as soon as possible, but do not double up. Take ex-lax only as long as needed to achieve results. Ex-lax uses dried leaves from plants of the Senna genus, which function as a laxative to relieve constipation. This drug is meant to be taken with plenty of water.