What Is Sodium Phosphate? Uses, Dosage, and What You Need to Know in 2026

Your doctor prescribed sodium phosphate — and now you want to understand exactly what it is, what it does, and how to take it safely. Here's a plain-English guide to everything you need to know about sodium phosphate, dibasic/sodium phosphate, monobasic (OsmoPrep) in 2026.

What Is Sodium Phosphate?

Sodium phosphate, dibasic/sodium phosphate, monobasic (brand name: OsmoPrep) is a prescription osmotic laxative used to clean the colon before a colonoscopy. It comes in tablet form — each tablet contains 1.5 grams of sodium phosphate (1.102 g monobasic + 0.398 g dibasic). A full course consists of 32 tablets.

Sodium phosphate is not the same thing as table salt (sodium chloride). Phosphate refers to a different kind of sodium salt — one that the body uses for energy, bone structure, and cellular function. At medicinal doses, sodium phosphate draws large amounts of water into the colon, triggering the bowel evacuation needed for a successful colonoscopy.

What Is Sodium Phosphate Used For?

Oral tablets (OsmoPrep): FDA-approved for colon cleansing prior to colonoscopy in adults. This is the form patients fill at the pharmacy.

IV injection: A separate form used in hospital settings to treat or prevent hypophosphatemia (dangerously low blood phosphorus levels) and as part of TPN (total parenteral nutrition) formulas for patients who cannot eat.

Enema/rectal (OTC historically): A rectal enema form (Fleet Enema) is available OTC for treating occasional constipation, though this is a different product and use than the colonoscopy prep tablets.

Who Makes OsmoPrep?

OsmoPrep is manufactured and marketed by Salix Pharmaceuticals. It was initially FDA-approved in 2006. It is available only by prescription. Generic versions of sodium phosphate monobasic/dibasic tablets are also available from manufacturers such as Lupin Pharmaceuticals.

How Do You Take OsmoPrep?

OsmoPrep must be taken in two split doses:

Dose 1 — Evening before your colonoscopy: Take 4 tablets with 8 oz of clear liquid every 15 minutes for a total of 20 tablets.

Dose 2 — Morning of your colonoscopy: Starting 3–5 hours before the procedure, take 4 tablets with 8 oz of clear liquid every 15 minutes for a total of 12 tablets.

You must drink a total of 2 quarts (64 oz) of clear liquid during the prep to stay hydrated. Clear liquids include water, clear broth, plain gelatin, and white grape juice. Avoid anything red, purple, or containing pulp — these can interfere with your colonoscopy results.

What Should You NOT Do During OsmoPrep Prep?

Do NOT take other laxatives or enemas containing sodium phosphate — doubled phosphate load significantly increases kidney damage risk.

Do NOT take oral medications within 1 hour before or after starting each OsmoPrep dose — absorption of those medications may be impaired.

Do NOT eat or drink alcohol, milk, red or purple beverages, or anything with food pulp during the prep.

Do NOT use OsmoPrep again within 7 days of a previous course.

Who Should NOT Take OsmoPrep?

OsmoPrep is not appropriate for everyone. Do not take it if you have:

Prior acute phosphate nephropathy (kidney damage caused by phosphate)

Kidney disease, heart failure, or significant electrolyte abnormalities

Bowel obstruction, perforation, toxic megacolon, or toxic colitis

A history of gastric bypass or stapling surgery

Allergy to sodium phosphate

Is Sodium Phosphate a Controlled Substance?

No. Sodium phosphate (OsmoPrep) is not a controlled substance. It does not have DEA scheduling. However, it is available only by prescription because of its boxed warning for acute phosphate nephropathy — a rare but serious kidney complication. Any licensed prescriber can write a prescription for it.

How Much Does OsmoPrep Cost?

Without insurance, a 32-tablet course of OsmoPrep typically runs $113–$305 at retail pharmacies. With a GoodRx coupon, you may pay as little as approximately $277 at certain pharmacies. Generic versions may be available at lower prices. Many commercial insurance plans cover OsmoPrep, though some require prior authorization or place it on a higher formulary tier.

If you need to find OsmoPrep at a pharmacy near you, medfinder can help locate it quickly. Curious about how sodium phosphate works? Read our companion post: how does sodium phosphate work — mechanism of action explained.