Spirulina dosing guide: how much to take, when, and for which goals

The standard adult dose

3–5 g/day is the dose range used in the majority of clinical trials demonstrating benefits for iron status, LDL/HDL cholesterol, fasting glucose, inflammatory markers (CRP, IL-6), and athletic endurance. Most adults can start here if they have no specific sensitivities.
1 g/day is an adequate starting dose for people new to spirulina or with a history of GI sensitivity. Increase by 1 g every 3–5 days toward your target dose.
Above 5 g/day: Higher doses (8–10 g/day) are used in some athletic performance studies and in specific therapeutic contexts. Benefits above 5 g/day are not proportionately larger for most goals — there is no established benefit to exceeding 10 g/day.

Iron status improvement: 3–5 g/day. Iron content approximately 2–4 mg/5 g as non-haem iron; absorption enhanced by vitamin C. Take with citrus juice or fruit. Benefits accumulate over 8–12 weeks — check ferritin at baseline and 12 weeks.
Immune support: 3–5 g/day. NK cell activation and IL-12 induction observed from 3 g/day in clinical studies. Note: NK stimulation is a contraindication concern in immunosuppressed individuals (see below).
Lipid improvement (LDL/HDL/triglycerides): 3–5 g/day. Reductions in total cholesterol and LDL, increases in HDL observed at 3–4.5 g/day over 12–16 weeks in multiple RCTs.
Blood sugar and metabolic syndrome: 3–5 g/day. Fasting glucose reductions and adiponectin increases observed in PCOS, type 2 diabetes, and metabolic syndrome studies at 3–8 g/day. Take with meals.
Athletic performance and endurance: 5–8 g/day. Higher dose range used in endurance studies showing VO²max improvement and reduced exercise-induced oxidative stress. Split doses (morning and pre-workout) used in practice.
Anti-inflammatory and antioxidant: 3–5 g/day of phycocyanin-rich spirulina. Phycocyanobilin is the active NOX2-inhibiting compound; higher phycocyanin content per gram means lower effective dose is possible with premium products.

Start at 0.5–1 g/day for the first week. This minimises the risk of GI adjustment symptoms (bloating, loose stools) that some people experience in the first 1–2 weeks.
Increase by 0.5–1 g every 3–5 days until reaching target dose. This applies particularly to people with IBS, IBD, mast cell activation syndrome, post-COVID fatigue, or a history of food sensitivities.
If any symptom increase occurs (fatigue, headache, GI upset): hold current dose for 5–7 days; do not increase until stable. This is particularly important in post-exertional malaise conditions (ME/CFS, long COVID).

Morning (before or with breakfast): Most commonly recommended timing. Spirulina contains tyrosine and phenylalanine — amino acid precursors to dopamine and noradrenaline — which can be activating. Morning timing avoids any stimulatory effect on sleep.
Split doses (morning + afternoon): Practical for larger doses (5–8 g/day) and for athletes taking one dose pre-workout. Ensures consistent phycocyanobilin availability across the day.
With or without food: Both are acceptable. Taking with food improves GI tolerance and may slow amino acid release. Taking 30 minutes before meals on an empty stomach may improve iron absorption (competitive absorption with other dietary minerals is reduced). For iron-deficient individuals: take 30 minutes before breakfast with a vitamin C source.
Not at bedtime: The activating amino acid content means spirulina is not suited to evening or bedtime use.

Powder: Most flexible for dose adjustment. A level teaspoon of standard spirulina powder is approximately 3–4 g (varies by brand particle size). Weigh with a digital scale for precision (especially for children or escalation protocols).
Tablets: Standard tablets are 500 mg each. Six tablets = 3 g; ten tablets = 5 g. Tablets are convenient for consistent daily doses but not suitable for children under 6 (choking risk) and require high water intake to dissolve comfortably.
Capsules: Typically 500 mg per capsule; same count as tablets for equivalent dose. Easier to swallow for those who find tablets difficult. Gelatin vs plant-based capsules: verify for vegan compliance.

Children: Toddlers (1–3 years): 0.5–1 g/day; preschool (3–6): 1–2 g/day; school age (6–12): 2–3 g/day; adolescents: 3–5 g/day. Always powder in food for under-6; verify heavy metal CoA before use.
Pregnancy: 3–5 g/day considered safe; ensure certified low-heavy-metal product; discuss with midwife or obstetrician.
CKD stage 3 (eGFR 30–59): Maximum 3–5 g/day; the potassium and phosphorus content (potassium ~400 mg/10 g, phosphorus ~120 mg/10 g) requires renal dietitian review. If on ACE inhibitor or ARB: monitor potassium at 2–4 weeks.
Immunosuppressed individuals: Any dose requires discussion with the prescribing specialist. Spirulina’s NK stimulation and IL-12 induction can oppose immunosuppressive regimens (organ transplant, rituximab/cyclophosphamide induction therapy, mycophenolate).
Haemochromatosis: Avoid unless iron is well-controlled by regular venesection. Spirulina’s iron content and potential ferritin elevation are contraindicated.
Post-COVID / ME/CFS: Start at 0.5 g/day; increase 0.5 g every 1–2 weeks; monitor 24–48h post-dose energy window. Exertion post-exertional malaise risk requires slow titration.

Active autoimmune flare on induction immunosuppression — defer until maintenance phase with specialist approval
Phenylketonuria (PKU) — spirulina’s phenylalanine content is contraindicated
Unconfirmed seafood allergy with cross-reactivity concern — start with a small test dose under medical supervision
On MAOIs (irreversible monoamine oxidase inhibitors) — tryptophan content requires caution; discuss with prescribing psychiatrist