GoLytely and MiraLAX are not the same product, but they share the same core ingredient: polyethylene glycol 3350 (PEG 3350), an osmotic laxative. The key difference is what else is in the formulation, how much you take, and what each one is designed to do.
Same Active Ingredient, Different Formulations
Both products use PEG 3350, which works by pulling water into the stool, making it softer and easier to pass. Your body doesn’t absorb PEG 3350 in any meaningful way. It stays in the gut and does its job through osmosis.
GoLytely, however, isn’t just PEG 3350. Each one-gallon packet contains 227.1 grams of PEG 3350 plus a carefully balanced mix of electrolytes: sodium sulfate, sodium bicarbonate, sodium chloride, and potassium chloride. These electrolytes are there to help prevent dangerous shifts in your body’s sodium, potassium, and other mineral levels when you’re flushing out your entire colon. MiraLAX contains only PEG 3350 with no added electrolytes.
Different Doses for Different Jobs
MiraLAX is an over-the-counter laxative sold for everyday constipation. A standard dose is 17 grams of powder, about one capful, mixed into any beverage. It’s designed to produce a gentle bowel movement within one to three days.
GoLytely is a prescription product designed for a completely different purpose: bowel preparation before a colonoscopy. The dose is enormous by comparison. You drink four liters (roughly a gallon) of the mixed solution, typically over several hours, to completely clean out the colon so a doctor can get a clear view during the procedure. That’s more than 13 times the amount of PEG 3350 in a single MiraLAX dose.
Why MiraLAX Gets Used for Colonoscopy Prep
If GoLytely exists specifically for bowel prep, you might wonder why so many doctors tell patients to buy MiraLAX and mix it with Gatorade instead. The answer is mostly about taste and tolerability. GoLytely has a salty, chemical flavor that many people find difficult to stomach. Between 5% and 15% of patients prescribed four liters of GoLytely don’t finish drinking it all, which can mean a poorly cleaned colon and a less effective colonoscopy.
The MiraLAX-Gatorade protocol has become a popular workaround. A typical version, like the one outlined by Cleveland Clinic, calls for mixing an entire 238-gram bottle of MiraLAX into 64 ounces of a clear sports drink (not red, orange, or purple), along with four bisacodyl stimulant laxative tablets taken separately. You drink half the evening before your procedure and the other half about six hours before.
This combination is widely used but not FDA-approved for colon cleansing. Over 14 million colonoscopies are performed each year in the U.S., and many gastroenterologists prescribe this regimen routinely, but its safety data is more limited than GoLytely’s.
The Electrolyte Question
The biggest medical concern with using MiraLAX instead of GoLytely for bowel prep is electrolyte balance. When you flush your colon with a massive dose of PEG 3350, you lose sodium, potassium, and other minerals along with the fluid. GoLytely’s built-in electrolytes are designed to replace what’s lost. MiraLAX has no electrolytes at all, which is why the protocol pairs it with a sports drink, though sports drinks contain far less sodium and potassium than GoLytely’s electrolyte packet.
A randomized clinical trial comparing the two approaches found that electrolyte changes from baseline were small with both methods but significantly worse with the MiraLAX-sports drink combination for sodium, potassium, and chloride levels. About 3.9% of patients using MiraLAX with a sports drink developed low sodium (hyponatremia), compared to 2.2% on the electrolyte-containing PEG solution. The difference wasn’t statistically significant in that study, but the researchers noted their sample size may have been too small to detect a clinically important difference.
For most healthy adults, this modest electrolyte shift isn’t dangerous. But for older adults, people with kidney disease, or those on certain medications that affect electrolyte balance, the distinction between the two products could matter more.
Taste and the Drinking Experience
GoLytely’s taste is notoriously bad. Patients describe it as something like flat, salty lemonade with no sugar. Common survival strategies include drinking it ice cold through a straw aimed at the back of the throat, chewing spearmint gum between glasses, or rinsing with mouthwash immediately after each cup.
MiraLAX, on its own, is nearly tasteless and dissolves into whatever liquid you mix it with. When combined with a flavored sports drink, the prep solution tastes far more tolerable for most people. This palatability advantage is the main reason the MiraLAX-Gatorade protocol became so popular in the first place, and why patients are more likely to finish the full volume.
Quick Comparison
- Active ingredient: Both contain PEG 3350
- Electrolytes: GoLytely includes sodium sulfate, sodium bicarbonate, sodium chloride, and potassium chloride. MiraLAX has none.
- Availability: GoLytely requires a prescription. MiraLAX is available over the counter.
- FDA-approved use: GoLytely is approved for bowel preparation before colonoscopy. MiraLAX is approved for occasional constipation.
- Volume: GoLytely requires drinking four liters. A daily MiraLAX dose is one capful (17 grams) in 8 ounces of liquid.
- Taste: GoLytely is salty and widely disliked. MiraLAX is virtually flavorless.
So while GoLytely and MiraLAX are built around the same molecule, they’re designed for very different situations. One is a gentle daily laxative you can grab off a pharmacy shelf. The other is a prescription-strength colon cleanser with electrolytes engineered to keep your body in balance during an aggressive bowel prep. They’re related, but they’re not interchangeable.