Spirulina
A blue-green algae (technically a cyanobacterium) sold in tablet or powder form. Rich in protein, B vitamins, and antioxidants. Of the supplements in this list, spirulina has one of the more consistent evidence bases for modest weight loss — it is one of only two supplements to reach 'high certainty' in a large 2023 meta-analysis.
Quick read · 3 min
A 2023 network meta-analysis of 111 randomised controlled trials found that spirulina produced 1.77 kg more weight loss than placebo — and notably, this was rated as HIGH certainty evidence, which is unusual for supplement research.
How it works
Proposed mechanisms include reduced appetite (possibly through phycocyanin, an anti-inflammatory pigment), improved lipid and glucose metabolism, reduced inflammation linked to obesity, and enhanced satiety from its high protein content relative to its calorie count.
What the evidence shows
A 2023 network meta-analysis of 111 randomised controlled trials found that spirulina produced 1.77 kg more weight loss than placebo — and notably, this was rated as HIGH certainty evidence, which is unusual for supplement research. Spirulina was one of only two supplements in the analysis to reach this level of evidence certainty. Additional benefits on cholesterol and blood pressure have also been reported in trials.
The trade-off
What this tends to offer:
- ✓High in protein (~60% by weight)
- ✓Contains B12 (rare in non-animal foods)
- ✓Generally well-tolerated
- ✓Affordable (~$15–$30/month)
What this involves:
- •No direct weight loss mechanism
- •Benefit limited to small sample trials
- •May cause nausea or stomach upset
- •Possible contaminants (heavy metals, microcystins) if quality control is poor
Safety
Generally safe for most adults. The main concern is sourcing — spirulina can be contaminated with toxic substances called microcystins or heavy metals if grown in contaminated water. Always buy from reputable, third-party tested brands. People with phenylketonuria (PKU) should avoid it — spirulina contains phenylalanine. People taking immunosuppressant drugs should speak to a doctor first, as spirulina may stimulate immune activity.
Written and maintained by one person · Built with agentic AI tools · Every number checked against the cited trial · Not medical advice
How this site is built →Last reviewed
In the Network meta-analysis of 111 RCTs (2023), Spirulina produced 1.77 kg more weight loss than placebo (95% CI: -2.77 to -0.78). Rated HIGH certainty evidence — one of only two supplements to reach this level in the analysis.
Community insights
These are personal experiences shared in public online communities — not medical advice.
“Powder is much cheaper than tablets but has a strong taste that many people dislike. Blend it into something strongly flavoured — dark berry smoothies work well.”
“Source quality really matters here — look for products tested by a third-party lab (NSF, USP, Informed Sport). Cheap bulk spirulina from unknown sources can contain contaminants.”
Common questions
After reading this page, most people compare this with other supplements, look at prescription options, or check what they can do today without a prescription.
Next step most people take
Built with agentic AI tools and not a substitute for medical advice
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