The best laxative to fully clean you out depends on whether you need a one-time thorough evacuation or relief from days of built-up constipation. For a complete clean out, magnesium citrate is the most widely used and effective over-the-counter option, working within 30 minutes to 6 hours. For less urgent but still significant constipation, polyethylene glycol (MiraLAX) is the top recommendation from gastroenterologists and works within one to three days.
Magnesium Citrate for a Full Clean Out
Magnesium citrate is the go-to choice when you want fast, thorough results. It’s a saline osmotic laxative, meaning it pulls large amounts of water into your intestines, softening everything inside and triggering strong contractions that push it all through. A single 10-ounce bottle is the standard dose, and most people start seeing results within 30 minutes to 6 hours.
This is the same type of laxative used as part of colonoscopy preparation, where the goal is a completely empty colon. It’s available without a prescription at virtually any pharmacy or grocery store, usually for just a few dollars. Drink it cold if you can. The taste is more tolerable chilled, and follow it with a full glass of water.
There’s a tradeoff for that speed and power: magnesium citrate can cause significant cramping, bloating, and urgent diarrhea. It also shifts your electrolyte levels, pulling sodium, potassium, and calcium out of balance. For most healthy adults, this is temporary and harmless. But if you have kidney problems, heart conditions, or already have high magnesium or potassium levels, magnesium citrate can be genuinely dangerous. It also carries a real risk of dehydration, so drink plenty of fluids before, during, and after.
MiraLAX for Reliable, Gentler Relief
Polyethylene glycol 3350, sold as MiraLAX and similar store brands, is the laxative the American Gastroenterological Association specifically recommends for chronic constipation. It works through the same basic principle as magnesium citrate (drawing water into the intestines) but does so more gradually. Expect results within one to three days rather than hours.
That slower timeline is actually the point. MiraLAX softens and loosens stool without the explosive urgency of stronger options. You dissolve one dose in a glass of water or juice and drink it once a day. The cramping is minimal for most people, and it doesn’t cause the sharp electrolyte swings that magnesium citrate does. If your constipation has been building for several days and you want thorough relief without spending the evening in the bathroom, this is the better fit.
For a more aggressive clean out using MiraLAX, some people use a higher-volume approach similar to colonoscopy prep: mixing a full cap of powder into a large bottle of a clear electrolyte drink and consuming it over several hours. This produces results closer to what magnesium citrate does but with better hydration. If you’re considering this approach, it’s worth checking with a pharmacist about the right amount for your situation.
Stimulant Laxatives: Bisacodyl and Senna
Stimulant laxatives like bisacodyl (Dulcolax tablets) and senna (found in brands like Senokot) work differently. Instead of pulling water in, they directly trigger the muscles in your intestinal wall to contract and push stool forward. They typically work within 6 to 12 hours, which makes them a good option to take before bed with results the next morning.
These are effective for constipation, but they’re not ideal as your only tool for a complete clean out. They move things along but don’t add the water content needed to fully soften and flush hardened stool. That’s why colonoscopy prep protocols often pair bisacodyl tablets with an osmotic agent like magnesium citrate: the osmotic laxative floods the intestine with water while the stimulant pushes everything through.
Stimulant laxatives tend to cause more noticeable cramping than osmotic options. They’re safe for occasional use, but using them daily over long periods can make your bowels less responsive on their own, creating a cycle of dependence. This is especially common in older adults, who sometimes end up on stimulant laxatives indefinitely without realizing they were only meant to be temporary.
What a Full Clean Out Actually Feels Like
If you’re using a strong osmotic laxative for a thorough clean out, plan to stay near a bathroom. After taking magnesium citrate or a high-volume MiraLAX prep, most people develop significant diarrhea within a few hours. Mild bloating and abdominal cramps are normal and expected. This is the medication doing exactly what it’s supposed to do.
The process typically plays out over 3 to 5 hours. Early bowel movements will look like loose stool, gradually becoming more watery and eventually clear or light yellow. That shift to watery, clear output is the sign that your colon is essentially empty. During this time, drink clear fluids steadily. Water, broth, and electrolyte drinks all help replace what you’re losing. Dehydration is the most common problem people run into, and it’s entirely preventable.
Choosing the Right Option for Your Situation
- Fastest full clean out: Magnesium citrate. Works in 30 minutes to 6 hours. Best for a one-time thorough evacuation when you need results today.
- Thorough but gentler: MiraLAX (polyethylene glycol). Works in 1 to 3 days at standard doses. The top clinical recommendation for constipation that’s been going on for a while.
- Overnight relief: Bisacodyl or senna tablets. Works in 6 to 12 hours. Good for moderate constipation, take at bedtime for morning results.
- Combined approach: An osmotic laxative plus a stimulant, taken several hours apart. This is essentially what medical bowel prep protocols use for the most complete results.
Staying Regular After a Clean Out
A clean out solves the immediate problem, but if constipation keeps coming back, fiber is the foundation for long-term prevention. The AGA recommends fiber supplementation as the first step for managing ongoing constipation. Psyllium (Metamucil) and methylcellulose (Citrucel) are the two most common options. Psyllium is more thoroughly studied, but methylcellulose tends to cause less gas and bloating.
Start with a small dose of whichever you choose and increase gradually over a week or two. Jumping straight to a full dose is a reliable recipe for bloating and gas. Equally important: fiber supplements only work if you’re drinking enough water. Without adequate fluid, extra fiber can actually make constipation worse by creating bulkier, harder stool. Aim for at least 8 glasses of water a day when using a fiber supplement, more if you’re active or in a warm climate.
If over-the-counter fiber and osmotic laxatives aren’t keeping things moving, prescription options exist. The AGA recommends several prescription medications for people who don’t respond to store-bought solutions, so persistent constipation is worth bringing up with a doctor rather than cycling through stronger and stronger laxatives on your own.