Chronic constipation — what works in what order
Most chronic constipation responds to a small set of well-evidenced interventions in a specific order, with prescription laxatives reserved for the cases where the supplement layer doesn't suffice. The supplement aisle around constipation is loud, but the actual evidence supports a much narrower protocol than the shelf would suggest.
Layer 1 — Soluble fibre and water
Psyllium husk
5–10 g/day to start, titrate up to 15–20 g/day; always with adequate water
The most-evidenced fibre for chronic constipation, with consistent positive trial signal across multiple meta-analyses. Psyllium retains water through the colon and increases stool weight directly. Two crucial details: titrate up over 2–3 weeks (going straight to 15 g/day commonly causes a transient worsening of bloating before the gut adjusts) and drink adequate water (psyllium that doesn't have water to bind to can paradoxically worsen constipation). Soluble fibre supplementation also blunts post-meal glucose spikes — sometimes a useful side benefit.
Kiwifruit (whole, two per day)
2 green kiwifruit daily, eaten whole including the skin if tolerated
Direct head-to-head trials have shown kiwifruit at two per day matches or modestly exceeds psyllium at standard doses for stool frequency and consistency in chronic constipation. The mechanism appears to involve actinidin (a natural protease) plus the soluble fibre and water content. Cheaper than supplements, easier to stick to, and adds dietary diversity. The skin contains additional fibre and is edible if tolerated.
Layer 2 — Osmotic agents
Magnesium oxide (or hydroxide / citrate)
300–500 mg elemental magnesium daily, divided AM and PM
The one situation in supplement medicine where magnesium oxide is the right form to choose — its osmotic action in the bowel is the desired effect, not a side effect. Effective and inexpensive. Magnesium hydroxide (milk of magnesia) is essentially the same intervention in liquid form. Magnesium citrate works similarly with somewhat better absorption. Avoid in significant kidney disease (eGFR < 30) — risk of hypermagnesemia.
Polyethylene glycol (PEG, e.g. MiraLax / Movicol)
17 g (one capful) daily, dissolved in water; titrate down once regularity is established
Not a "supplement" in the strict sense, but worth noting because it is the OTC intervention with the strongest trial base in chronic constipation, including in pregnancy and in long-term use. Larger trials have shown clear benefit over placebo on essentially every endpoint that matters. Cheaper than most supplements; usually well tolerated. Reasonable alternative if magnesium oxide isn't sufficient.
Layer 3 — Targeted probiotic strains
Bifidobacterium lactis HN019
1.8 × 10⁹ CFU/day for at least 4 weeks
One of the few probiotic strains with positive RCT signal specifically for whole-gut transit time and stool frequency in adults with chronic constipation. Strain specificity matters here — generic "probiotic blends" do not have the same evidence. Effect develops over 2 to 4 weeks. Generally well tolerated; mild bloating in the first week is the most common complaint.
Layer 4 — Magnesium-rich and water-rich food layer
Distinct from the supplement layer but worth flagging because the lifestyle inputs do most of the heavy lifting in functional constipation: magnesium-rich foods (leafy greens, almonds, pumpkin seeds, dark chocolate), prunes (the only fruit with as much constipation-specific RCT evidence as psyllium), adequate fluid intake (target ~30 mL per kg body weight if tolerated), and physical activity (genuinely matters; sedentary populations have higher constipation prevalence in cohort data).
What to skip
- Senna and stimulant-laxative supplements (long-term) — Senna is fine occasionally; daily long-term use causes dependence and an increasingly atonic colon. Senna-based "detox teas" with daily dosing are particularly worth avoiding.
- "Colon cleanse" multi-ingredient products — typically combine senna with herbal stimulants and magnesium at undisclosed proportions.
- Castor oil — an obsolete intervention with cramping, dehydration, and electrolyte risks. Not appropriate for chronic use.
- Generic high-CFU probiotic blends — strain-specific evidence is what matters for transit; "more strains, more CFU" does not translate.
- Insoluble-fibre supplements (wheat bran) — can worsen bloating and pain in functional constipation, particularly when the underlying issue is slow transit or pelvic-floor dysfunction.
The non-supplement layer that often matters more
Several functional-constipation patterns respond poorly to supplements because the underlying issue isn't transit time. Pelvic-floor dysfunction (the muscles don't relax appropriately during defecation) responds to biofeedback therapy and is missed often. Slow-transit constipation can require prescription prokinetics (linaclotide, plecanatide, prucalopride). Opioid-induced constipation has its own targeted treatments. If the protocol below isn't working at 6 to 8 weeks, the next conversation is with a gastroenterologist about cause workup, not stacking more supplements.