While the effects of most laxatives vary depending on the brand, they are usually gone within 24 hours. According to multiple HealthTap contributors, most lose their effectiveness after eight hours.
According to WebMD, while mineral oil and other lubricant laxatives allow for fast expulsion, fiber-based laxatives and stool softeners are gentler on the body and can take up to a week to fully work. Other osmotic laxatives, such as Milk of Magnesia, suck water from the colon and require many glasses of drink to attain their full capacity. Ex-Lax and other stimulant laxatives may cause a rapid bowel movement, but long-term use can lead to dependency.
Read more: What Is “24KGB” and What Does It Mean?