The fastest over-the-counter option for a bowel movement is a saline osmotic laxative like magnesium citrate liquid, which typically produces results within 30 minutes to 6 hours. If you need relief today, that’s the place to start. But several other options exist depending on how quickly you need to go and what you have on hand.
Fastest Options: Under 6 Hours
Magnesium citrate liquid is the speed king of drugstore laxatives. It works by pulling water into your intestines, which softens stool and triggers contractions. Most people have a bowel movement within 30 minutes to 6 hours of drinking it. You can find it at any pharmacy, usually in a glass bottle near the digestive health aisle. Drink it with a full glass of water, since it can cause dehydration and increased thirst.
Bisacodyl suppositories are another fast-acting option. Because they’re inserted rectally rather than swallowed, they bypass the digestive tract and work directly on the lower colon. Most people get results within 15 to 60 minutes. If the idea of a suppository doesn’t bother you, this is one of the quickest ways to get things moving.
Coffee works surprisingly fast for some people. About 29% of adults experience a laxative effect from coffee, and research published in the journal Gut found that it increases colon activity within four minutes of drinking it. That effect lasts at least 30 minutes. Interestingly, decaf coffee produced a similar response, suggesting it’s not just the caffeine doing the work. If you’re one of the people coffee affects this way, a cup on an empty stomach may be all you need.
Same-Day Relief: 6 to 12 Hours
Stimulant laxatives like senna and bisacodyl tablets are the classic “take it at night, go in the morning” option. Senna works in 6 to 12 hours, and bisacodyl tablets take about 10 to 12 hours. They work by stimulating the muscles in your intestinal wall to contract and push stool through. These are widely available as generic tablets and are inexpensive.
Gastroenterology guidelines from the AGA and ACG recommend stimulant laxatives as a good “rescue” option for short-term use, like when you’re constipated from traveling or from a medication side effect. They’re not meant for daily, long-term use.
Slower but Gentler: 1 to 3 Days
If your constipation isn’t urgent and you’d prefer a softer approach, several options work over one to three days. These are better suited for mild or recurring constipation than for “I need to go right now.”
- Osmotic laxatives like polyethylene glycol (MiraLAX): This powder dissolves in water and draws fluid into the colon. It typically works in 1 to 3 days without causing sudden urgency. You take it once daily for up to 7 days.
- Stool softeners: These add moisture to stool so it’s easier to pass. They take 12 hours to 3 days and are most useful when straining is the main problem rather than infrequency.
- Fiber supplements (psyllium): Among fiber supplements, only psyllium has strong evidence of effectiveness. It absorbs water to form soft, bulky stool that’s easier for your intestines to move along. You need to drink plenty of water with it, or it can actually make constipation worse. Expect gas, especially in the first few days.
Food and Drinks That Help
Prune juice contains sorbitol, a sugar alcohol that pulls water into the intestines and acts as a natural osmotic laxative. In one study, drinking about 125 mL (roughly half a cup) twice daily produced a mild laxative effect. That’s about one full cup per day total. Whole prunes work similarly and also provide fiber. The effect isn’t as fast or predictable as a pharmacy laxative, but for mild constipation, prune juice is a reasonable first try.
Warm liquids in general can help stimulate the gastrocolic reflex, which is the natural wave of contractions your colon makes after your stomach stretches. Drinking a large glass of warm water or hot tea first thing in the morning takes advantage of this reflex when it’s strongest.
What to Avoid
Using fast-acting laxatives regularly can cause problems. Oral laxatives interfere with how your body absorbs certain medications and nutrients. Long-term use of stimulant laxatives or stool softeners can lead to electrolyte imbalances, affecting minerals like potassium, sodium, and magnesium that regulate your heart rhythm, muscle function, and brain activity. Severe imbalances can cause weakness, confusion, heart rhythm changes, and seizures.
The general rule: stimulant laxatives are for occasional use, not a daily habit. If you’re reaching for them more than once a week, the constipation itself needs attention rather than just the symptom.
Signs Something More Serious Is Happening
Most constipation is uncomfortable but harmless. However, certain symptoms point to a possible blockage or fecal impaction that laxatives won’t fix and could make worse. If you have sudden constipation with abdominal cramps and you can’t pass gas or stool at all, do not take a laxative. That combination can signal a bowel obstruction. Blood in the stool, very thin pencil-like stools, or persistent diarrhea following a long stretch of constipation also warrant a call to your doctor. A complete bowel blockage or severely impacted stool sometimes requires medical removal.