Spirulina has been studied in various contexts, but “natural” does not mean risk-free. Common complaints are gastrointestinal: bloating, gas, nausea, diarrhea/constipation. Some people report headaches or mild skin reactions.\n\nA key risk domain is product quality and contamination. Microalgae products can vary in heavy metals or unwanted toxins depending on sourcing and manufacturing. Choose reputable brands with quality testing.\n\nIf you have autoimmune disease, consult a clinician due to theoretical immune-activation concerns. If you use anticoagulants or combine multiple botanicals, discuss bleeding-interaction risk. Pregnancy, breastfeeding, and pediatric use require medical guidance.\n\nBottom line: often tolerated, but quality and individual risk factors matter.