Laxatives (Bulk, Osmotic, Stimulant, Prokinetic)
Different types treat different kinds of constipation. Polyethylene glycol (PEG) is first-line and safe for daily use. Stimulant laxatives are for short-term only.
This article is educational and does not replace your doctor's advice. Seek urgent care for any red-flag symptoms.
Drug class
Laxatives — multiple subclasses
Examples
Bulk: psyllium (Metamucil, Fybogel), methylcellulose. Osmotic: PEG (Movicol, Forlax, Miralax), lactulose, magnesium hydroxide. Stimulant: senna (Senokot), bisacodyl (Dulcolax). Prokinetic: prucalopride (Resolor), linaclotide (Linzess), lubiprostone.
How it works
Different mechanisms: Bulk laxatives absorb water and add bulk to stool. Osmotic laxatives pull water into the bowel. Stimulant laxatives trigger intestinal contractions. Prokinetics speed up colonic transit by acting on serotonin receptors.
What it treats
- Functional constipation
- IBS-C
- Opioid-induced constipation
- Bowel preparation for colonoscopy (high-dose PEG)
- Hard stools that cause hemorrhoids or fissures
How to take it
Psyllium — start at 1 teaspoon daily, mix in 240 mL water, drink IMMEDIATELY before it thickens. Gradually increase to 1 tablespoon (5-10 g). Drink lots of water.
PEG — 17 g (one sachet) mixed in 250 mL water once daily. Adjust to 1-2 sachets/day for 1-3 soft stools. Safe long-term.
Senna or bisacodyl — for short-term use only (a few days). Take at bedtime; works overnight.
Prucalopride — 2 mg daily (1 mg in elderly). Taken in the morning.
Common side effects
- Bulk laxatives: bloating, gas (often improves over weeks)
- Osmotic laxatives: bloating, sometimes loose stools if too much
- Stimulant laxatives: cramping, occasional electrolyte issues with long-term use
- Prokinetics: headache (common in first week), nausea, diarrhea
Serious side effects — call your doctor
Severe abdominal pain or vomiting
Possible obstruction or other serious cause — stop laxative and see doctor.
No bowel movement after several days of treatment
Possible obstruction — investigate.
Heart palpitations or muscle weakness with chronic stimulant use
Possible electrolyte imbalance — needs blood test.
Interactions
Bulk laxatives reduce absorption of other medications — separate by 2 hours. Magnesium-containing laxatives can interact with kidney drugs. Most other laxatives have few significant interactions.
Monitoring
No monitoring for short-term use. Long-term high-dose stimulant laxative use: check potassium and magnesium yearly. Long-term lactulose: check electrolytes if also on diuretics.
When and how to stop
Step-down approach: once regular soft stools achieved, reduce dose gradually. Stimulant laxatives: stop within 1-2 weeks unless under medical supervision. PEG: safe to continue indefinitely.
Pregnancy & breastfeeding
PEG and bulk laxatives are first-line in pregnancy and generally safe. Avoid stimulant laxatives in pregnancy unless necessary. Consult your obstetrician.
Questions to ask your doctor
Save this list or print it before your appointment — doctors appreciate prepared patients.
- Which laxative is best for me?
- Is PEG safe long-term?
- Can I become "dependent" on stimulant laxatives?
Medically reviewed by: SGA Patient Education Panel · Last reviewed 24/04/2026