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
- •Evidence: Moderate — some consistent evidence but with limitations
- •A 2023 network meta-analysis of 111 randomised controlled trials found that spirulina produced 1.
- •Generally safe for most adults.
- •Unlike prescription drugs, supplements are not tested for effectiveness by the FDA before sale
Based on clinical trials · No rankings · Every claim linked to source
Last reviewed: March 2026
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.
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.
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.