A small but carefully designed clinical trial suggests that a daily gram of spirulina may take the edge off anxiety and stress. The catch is that the participants were a very specific group: men receiving methadone maintenance therapy (MMT) for opioid dependence. The findings are interesting, but they should be read with that context firmly in mind.
What the researchers did
The study, published in Food Science & Nutrition in 2026 by Asadolah-Poor-Kashi and colleagues, was a double-blind, randomized, placebo-controlled trial. Fifty men in methadone maintenance therapy were split evenly into two groups of 25. One group took spirulina at 500 mg twice daily, for 1 gram per day in total. The other group took a placebo. The intervention lasted 12 weeks, with assessments at baseline and at the end of the trial.
The trial was registered in advance (IRCT20231101059923N2, registered December 2023). Prospective registration is a good sign, because it limits the room for outcomes to be swapped or cherry-picked after the fact.
The team measured a broad set of outcomes:
- Psychological distress: the Depression, Anxiety, and Stress Scale-21 (DASS-21)
- Sexual function: the International Index of Erectile Function (IIEF)
- Drug craving: the Drug Desire Questionnaire (DDQ)
- Cognition: the FAS verbal fluency test, the Iowa Gambling Task (IGT), and the Trail Making Test (TMT)
What they found
Spirulina significantly reduced anxiety and stress scores compared with placebo (p < 0.05). That is the headline result.
The other outcomes did not move. There were no significant between-group differences in depression, sexual function, drug craving or cognitive performance (all p > 0.05). The abstract does not report effect sizes, so it would be a mistake to guess at how large the improvement in anxiety and stress actually was. All we can say is that it reached statistical significance.
Why this population matters
People on methadone maintenance often deal with elevated anxiety, stress and other psychological problems, along with sexual dysfunction and cognitive difficulties. These problems can undermine treatment and retention. That makes low-risk supportive interventions attractive in principle.
It also means the results may not transfer to the general population. This trial enrolled only men, only people on methadone, and only 50 of them. Anxiety and stress in a person managing opioid dependence have different drivers than everyday work stress or generalized anxiety in someone who is not on opioid therapy. Whether spirulina would do the same for other groups, or for women, is simply not answered here.
How to read the result
A few points call for caution:
- Small sample. With 25 people per arm, the trial is vulnerable to chance findings. The authors themselves call for larger studies.
- Mixed results. Of the several outcome domains, only two (anxiety and stress) showed benefit. When many outcomes are tested, an occasional significant result can appear by chance, so replication matters.
- Short follow-up. Twelve weeks says nothing about longer-term effects.
- No mechanism shown. The abstract does not establish why spirulina might help. Proposed explanations for algae-derived supplements often involve antioxidant or anti-inflammatory activity, but that remains speculative here.
The absence of effects on depression, craving and cognition is also informative. Spirulina is not shown here to be a general mental-health booster, a craving suppressant or a cognitive enhancer. The authors describe it only as a potential supportive intervention for anxiety and stress.
Practical takeaways
Dose and duration. The trial used 500 mg twice daily (1 g per day) for 12 weeks. If you are curious about spirulina, that is the only regimen with evidence behind it in this study. More is not necessarily better, and this trial does not support higher doses.
Quality matters. Spirulina is a cyanobacterium grown in ponds or tanks, and it can be contaminated. Poorly sourced products may contain heavy metals or microcystins, which are toxins produced by other cyanobacteria growing alongside it. Look for products with third-party testing for heavy metals and microcystins, clear sourcing, and batch certificates of analysis. Cheap, unverified products are a gamble. Also note that the product used in the trial may differ from what you find on a shelf.
Who might consider it. Healthy adults with mild stress who want to try a low-risk supplement could reasonably be curious, but the evidence for them is indirect. For people on methadone or other medications, the decision should involve their prescriber or addiction-treatment team. Spirulina should never replace prescribed treatment, counseling or anxiety care. People with autoimmune conditions, phenylketonuria or on immunosuppressants should also check with a clinician, since spirulina is generally advised against or used cautiously in these situations.
Bottom line
This randomized, double-blind trial gives preliminary evidence that 1 g/day of spirulina for 12 weeks can lower anxiety and stress in men on methadone maintenance therapy. It does not show benefits for depression, sexual function, craving or cognition, and it cannot be extended to the general population. Treat it as a promising signal that justifies larger, longer trials, not as a reason to expect a calming effect from every bottle of green powder.
