Best Natural Laxative: Kiwi, Prunes, Psyllium or Magnesium?

The best natural laxative for most people is two kiwifruit a day, with prunes and psyllium as close equals. In a US trial that compared all three for four weeks, each one increased complete bowel movements, and kiwi caused the fewest side effects^[1]. Magnesium oxide has the strongest supplement data, while magnesium citrate is a short-term saline laxative^[2][3].

Below, the four are compared on the amounts used, the size of the effect, how fast each works and who should skip it. If your symptoms have lasted for months, our guide to chronic constipation covers causes, tests and the role of the gut microbiome.

Get medical help promptly if your constipation comes with blood in your stool or bleeding from your rectum, constant belly pain, vomiting or an inability to pass gas, or weight loss you cannot explain^[4]. These need a clinician, not a home remedy.

What is the most powerful natural laxative?

No single option wins every outcome, but kiwi has the best balance of benefit and comfort. In the 79-person US trial, the share of people who gained at least one complete bowel movement a week was similar for two green kiwis, 100 g of prunes and 12 g of psyllium daily^[1]. Fewer people were dissatisfied with kiwi than with the other two.

The two main guidelines line up with this:

• The 2025 British Dietetic Association guideline, built on 75 randomized trials, makes recommendations for psyllium, kiwifruit, prunes, rye bread, high-mineral water and magnesium oxide^[2].
• The 2023 AGA-ACG guideline gives fiber, senna and magnesium oxide conditional recommendations, and its strongest recommendations go to medicines such as polyethylene glycol (PEG)^[5].
• A systematic review of 41 trials of over-the-counter products rated the evidence for psyllium, magnesium salts and fruit-based laxatives (kiwi, prunes, mango, figs) as moderate^[6].

On paper, magnesium oxide is the most powerful: it raised the chance of benefit more than threefold (RR 3.32), against RR 1.82 for psyllium^[2]. The gentlest well-studied option is kiwi.

Kiwi vs. prunes vs. psyllium vs. magnesium at a glance

Kiwi for constipation

Two kiwis a day is the best-studied fruit option. In an international trial of 184 people, two green kiwis daily for four weeks added 1.53 complete bowel movements a week in functional constipation and 1.73 in IBS with constipation, with no significant side effects^[7]. The comparison was 7.5 g of psyllium a day.

Gold kiwis also work. In a smaller New Zealand trial, two gold kiwis a day were as effective as fiber-matched psyllium and reduced straining^[8]. Both trials had funding or advisory links to the kiwifruit industry, which is worth knowing.

A meta-analysis of seven trials (399 people) rated the overall evidence for kiwi as low certainty and called for larger studies^[12]. The British guideline still recommends 2 to 3 kiwis daily for at least 4 weeks, and suggests kiwi over psyllium for people who get bloating, pain or gas from fiber^[2].

Why it may work is not fully understood. Kiwi's fiber, including pectin, holds water, and researchers have proposed effects on gut motility, the gut microbiota and colonic methane as other pathways^[13]. Those mechanisms are hypotheses, not proven.

Prunes: how they compare

Prunes are a fair match for psyllium. In a 40-person crossover trial, 50 g of prunes twice a day improved weekly complete bowel movements and stool consistency more than psyllium at the same fiber dose^[14]. A later meta-analysis found no difference between prunes and psyllium on stool frequency^[15].

Prunes also change stool output in people who are not constipated. In 120 healthy adults with low fiber intakes, 80 to 120 g of prunes a day for four weeks increased stool weight and frequency, but also flatulence^[10]. That trial saw a greater rise in Bifidobacterium species, though no change in short-chain fatty acids.

For amounts, timing and the juice version, see our guide to prune juice for constipation.

Psyllium: the best-studied fiber

Psyllium is the fiber supplement with the most consistent results. A meta-analysis of 16 trials (1,251 adults) found that fiber raised the chance of a response by 48%, with psyllium and pectin driving the effect on stool frequency^[16]. Doses above 10 g a day and courses of at least four weeks worked best.

The trade-off is gas. Fiber groups had more flatulence than control groups^[16], and psyllium had the most side effects in the three-way US trial^[1]. The British guideline advises raising fiber supplements gradually, week by week, and drinking extra fluid with them^[2].

Our psyllium husk page covers how it works in the gut, and our best fiber supplement comparison covers which fibers cause the most gas.

Magnesium citrate vs. magnesium oxide for constipation

Magnesium oxide is the form with placebo-controlled trials for chronic symptoms. Magnesium citrate liquid is a saline laxative for an occasional, faster clear-out^[3]. Both pull water into the bowel; NIH describes the laxative effect of magnesium salts as osmotic^[17].

Magnesium oxide

• In a double-blind trial of 34 women, 1.5 g a day for 28 days led to overall improvement in 70.6% vs. 25.0% on placebo^[18].
• In a 90-person trial, 1.5 g a day matched senna (68.3% vs. 69.2% improved), compared with 11.7% on placebo^[19].
• The British guideline suggests starting at 0.5 g a day and increasing weekly, up to 1.5 g, for at least 4 weeks^[2].

Both trials were small and done in Japan, and the AGA-ACG panel graded its magnesium oxide recommendation as conditional^[5].

Is magnesium citrate a good immediate laxative?

It is the fastest option here, though not instant. The label we read in October 2026 says the liquid generally produces a bowel movement in 30 minutes to 6 hours^[3]. It is for occasional constipation. Ask a doctor first if you have kidney disease, are on a magnesium-restricted diet, or have used a laxative for more than a week.

Who should be careful with magnesium

Excess magnesium is cleared by the kidneys, so the risk of magnesium toxicity rises with impaired kidney function^[17]. A review of magnesium oxide urges attention to dose, blood magnesium levels and drug interactions, especially in older adults^[11]. Magnesium can also bind some antibiotics (tetracyclines and quinolones), which should be taken at least 2 hours before or 4 to 6 hours after it^[17].

What helps you poop within 30 minutes?

Among natural options, only magnesium citrate liquid has a same-day timeframe, at 30 minutes to 6 hours on its label^[3]. Kiwi, prunes, psyllium and magnesium oxide were all measured over weeks, not hours^[1][18]. Fiber supplements gave the best results after at least four weeks of daily use^[2].

If you need relief today and food has not helped, a pharmacist can explain the faster over-the-counter options. Our comparison of stool softeners, laxatives and fiber explains how each class works and how long it takes.

How do natural laxatives work?

Natural laxatives work in three main ways: they add water-holding bulk, pull water into the bowel, or may speed gut movement.

1. Bulk and water. Psyllium increased both stool frequency and stool softness in the British guideline's meta-analyses^[2].
2. Osmosis. Unabsorbed magnesium salts draw water into the intestine and colon^[17].
3. Motility and microbes. Kiwi compounds may act on gut motility and the microbiota, though this is still being worked out^[13]. Prunes raised Bifidobacterium counts in one trial^[10].

The microbiome angle has limits. The British guideline found no convincing evidence to recommend any specific probiotic strain for constipation^[2]. Our review of probiotics for constipation goes strain by strain.

What foods act like a natural laxative?

Kiwi and prunes are the natural laxative foods with the most trial data, and two less obvious options have trials too^[2]. Here is what each study used:

The details behind the less familiar options:

• Rye bread: 6 to 8 slices a day for at least 3 weeks added about 0.43 bowel movements a week compared with white bread. The guideline notes that this much bread may not be realistic^[2].
• High-mineral water: 0.5 to 1.5 liters a day for 2 to 6 weeks raised the response rate (RR 1.47) compared with low-mineral water^[15][2]. The waters studied had 1,530 to 2,000 mg/L of sulfate, against 3 to 112 mg/L in UK tap water^[2].
• Senna: this plant-based stimulant laxative matched magnesium oxide in one trial^[19]. In the British meta-analysis, though, 83% of people on senna in one study needed a lower dose because of pain or diarrhea^[2]. NIDDK advises stimulants only when constipation is severe or other treatments have failed^[20].

For everyday fiber from food, adults need 22 to 34 g a day depending on age and sex^[20]. Our list of high-fiber foods for constipation ranks foods by grams per portion, and our coffee and bowel movements post covers that morning effect.

When to see a doctor

See a clinician promptly, rather than trying another remedy, if you have any of these^[4][3]:

• bleeding from your rectum or blood in your stool;
• constant belly pain, vomiting, fever or lower back pain;
• you cannot pass gas, or you have no bowel movement after a laxative;
• weight loss you cannot explain;
• a sudden change in bowel habits that lasts more than 2 weeks.

Also check with your doctor before using magnesium if you have kidney disease^[17]. If you think a medicine is causing your constipation, do not stop or change it without talking to your prescriber^[20].

This article is for general educational purposes and is not medical advice. Doses are those used in studies or printed on the label we retrieved in October 2026, not personal recommendations. Talk to a qualified healthcare professional before using laxatives or supplements, particularly if you are pregnant, immunocompromised, taking prescription medication, or managing a diagnosed condition such as kidney disease.