Dulcolax (Bisacodyl) 5 mg Tablets and 10 mg Suppositories: OTC Stimulant Laxative for Constipation and Bowel Preparation

Information last reviewed: May 2026 — for educational purposes only.

Dulcolax (bisacodyl) is an over-the-counter stimulant laxative used for relief of occasional constipation and as part of bowel preparation regimens prior to colonoscopy or other lower GI procedures. Bisacodyl is a prodrug — it is converted by intestinal bacteria and enzymes to its active diphenol form in the colon, where it acts on the enteric nervous system to directly stimulate colonic peristalsis (rhythmic muscular contractions that propel bowel contents). It also increases water and electrolyte secretion into the colonic lumen, which softens stool and contributes to its laxative effect. The result is a reliable, predicable bowel movement within 6–12 hours of oral dosing or 15–60 minutes of rectal use.

Bisacodyl is specifically formulated as enteric-coated tablets to prevent dissolution in the stomach — it must reach the small intestine intact where hydrolysis converts it before it reaches the colon. This means the tablets must never be crushed, chewed, or dissolved, and must not be taken within one hour of milk, antacids, or medications that raise gastric pH, as these destroy the enteric coating and release bisacodyl prematurely in the stomach (causing gastric irritation, nausea, and loss of efficacy).

What Is Bisacodyl?

Bisacodyl (brand: Dulcolax, Carter's Little Pills, Fleet Bisacodyl) is a diphenylmethane stimulant laxative — the same class as cascara sagrada and senna, though structurally different. It stimulates nerve endings in the colonic mucosa (via the enteric nervous system) to increase peristaltic contractions. It is available in oral tablet and rectal suppository forms — each offering a different onset time for different clinical needs. It is one of the most commonly used laxatives worldwide and is included in most bowel preparation protocols for colonoscopy alongside osmotic agents (PEG solutions).

OTC Availability

Bisacodyl 5 mg tablets and 10 mg suppositories are available over the counter in the US without a prescription. No physician visit is required for occasional OTC use but chronic constipation lasting more than two weeks should prompt medical evaluation to identify underlying causes.

Strengths and Available Forms

• 5 mg enteric-coated tablets (oral) — adults: 1–3 tablets (5–15 mg) once daily at bedtime; onset 6–12 hours; children 6–12 years: 1 tablet; must NOT be crushed, chewed, or taken with milk/antacids within 1 hour
• 10 mg rectal suppository — adults and children ≥12 years: 1 suppository rectally; onset 15–60 minutes; ideal when rapid evacuation required (e.g., morning of procedure); children 6–12 years: 5 mg (half suppository)
• Bisacodyl enema (liquid rectal solution) — some formulations available for rapid rectal stimulation where suppositories are not preferred

Important administration rules for tablets: Swallow whole with a full glass of water. Do not take within 1 hour of drinking milk or taking antacids, proton pump inhibitors, or H2 blockers. Do not take within 1 hour of any dairy product or alkalinising agent. Taking tablets with milk or antacids destroys the enteric coating in the stomach, releases bisacodyl prematurely, and can cause cramping, nausea, and loss of efficacy.

Bowel preparation: For colonoscopy, bisacodyl tablets are often prescribed the evening before the procedure in combination with a large-volume polyethylene glycol (PEG) osmotic solution taken the following morning. The combination provides more thorough cleansing than PEG alone for most patients.

Price of Dulcolax

Generic bisacodyl tablets and suppositories are among the lowest-cost OTC laxatives available. Brand-name Dulcolax is affordable and widely available at pharmacies, grocery stores, and online. No prescription required. Cost is comparable between brand and generic.

Frequently Asked Questions

Why must bisacodyl tablets be swallowed intact and not taken with milk?

Bisacodyl tablets are protected by a special enteric coating designed to prevent breakdown in the acidic stomach environment — the tablet must pass through the stomach undissolved and release only in the alkaline environment of the small intestine, where enteric bacteria activate the drug. Crushing, chewing, or exposing the tablet to alkaline substances (milk, antacids, PPIs) in the stomach destroys the enteric coating. This causes premature drug release in the stomach, leading to gastric irritation, nausea and cramps without effective bowel stimulation, and potential loss of efficacy. This is the most commonly cited administration error with bisacodyl and should be clearly communicated to every patient.

Is it safe to use Dulcolax regularly for chronic constipation?

Bisacodyl (like all stimulant laxatives) is intended for occasional use (generally no more than 7 consecutive days). Chronic daily use of stimulant laxatives can potentially lead to electrolyte imbalances (especially potassium loss), reduced gut motility over time, and cathartic colon syndrome with very long-term abuse. For chronic constipation, osmotic laxatives (polyethylene glycol, lactulose) are generally preferred for regular use as they are gentler and have a better safety profile for ongoing use. Bulk-forming laxatives (psyllium) are also suitable for daily long-term use. Persistent constipation warrants physician evaluation.

Can bisacodyl be used to prepare the bowel before a colonoscopy?

Yes — bisacodyl is a standard component of many colonoscopy bowel preparation protocols. Typical protocol: 2–3 bisacodyl 5 mg tablets taken orally the evening before procedure (usually around 6 PM), followed the next morning by the prescribed volume of a PEG-based electrolyte solution (typically 2–4 litres). The bisacodyl stimulates the descending colon while the PEG flushes the entire colon osmotically. The combination is well-validated in comparative studies with high rates of adequate or excellent bowel preparation, which is critical for polyp detection during colonoscopy.

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