Evidence explainerSpermidine

Is Spermidine Safe? Small Trials up to 40 mg a Day Found No Problems

Spermidine trials are small and short, but none found safety problems, including one at 40 mg a day. The bigger surprise is how little reaches the blood.

By Kymata Health editorial teamPublished October 9, 2026Last reviewed October 9, 2026

Medical review pending. Written by our editorial team from the studies cited below; a credentialed clinician has not reviewed it yet. Educational only, not medical advice.

Key takeaways

  • At 40 mg/day for up to 28 days, 37 healthy men showed no significant changes in clinical, lipid or blood-count measures and no product-related adverse events [1].
  • Over 12 months at 0.9 mg/day, adverse events were balanced between spermidine and placebo in 100 older adults [2].
  • At 1.2 mg/day for 3 months, vital signs, weight, blood safety tests and self-reported health did not differ from placebo [3].
  • Neither 15 mg nor 40 mg a day substantially raised blood spermidine [4][1].
  • The longest high-amount trial lasted 28 days, so longer-term safety at that amount is unknown [1].

The evidence, graded

Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.

  • Grade DNo effectSafety and blood polyamines at a high amountSpermidine · RCT · n=37 · 2024 · PMID 39405978No significant changes in clinical, lipid, chemistry or blood-count measures versus placebo and no product-related adverse events. Serum and urine polyamines did not change substantially.
  • Grade CNo effectMemory performance (mnemonic discrimination)Spermidine · RCT · n=100 · 2022 · PMID 35616942No significant change in memory performance or secondary outcomes versus placebo. Adverse events were balanced between groups.
  • Grade DMixedBlood spermidine and spermine levelsSpermidine · Crossover RCT · n=12 · 2023 · PMID 37111071Plasma spermine rose versus placebo, but plasma spermidine and putrescine did not change, and saliva levels were unaffected.

What the safety trials found

The highest amount tested was 40 mg/day of high-purity spermidine trihydrochloride for 7 and 28 days in 37 healthy men aged 50 to 70 [1]. It caused no significant changes in clinical, lipid, chemistry or blood-count measures versus placebo, and no product-related adverse events [1].

At lower amounts from wheat germ extract, a 3-month trial in 30 adults aged 60 to 80 (1.2 mg/day) found no differences from placebo in vital signs, weight, blood chemistry, blood counts or self-reported health, with compliance above 85% [3]. In the 12-month trial (0.9 mg/day), adverse events were balanced between groups [2].

Why blood levels barely move

In a 5-day crossover trial in 12 healthy volunteers, 15 mg/day raised plasma spermine but not spermidine [4]. At 40 mg/day, serum and urine polyamines did not change substantially, which the authors read as tight homeostatic control [1].

The limits of the data

All of these trials were small, the largest enrolling 100 people [2]. The 40 mg/day trial was exploratory and lasted 28 days [1]. Anyone taking prescription medicines, pregnant or managing a chronic condition should talk to a clinician before adding spermidine.

For what the trials found on memory, read spermidine benefits.

Quick answers

Is spermidine made from sperm?

The supplements in these trials were a wheat germ extract or a high-purity spermidine trihydrochloride [2][1].

What side effects were reported?

The trial abstracts report no product-related adverse events at 40 mg/day and balanced adverse events over 12 months, without listing specific effects [1][2].

Is a high-dose spermidine product better absorbed?

Not according to blood levels: 15 mg/day did not raise plasma spermidine, and 40 mg/day did not substantially change serum polyamines [4][1].

Keep reading

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References

  1. [1]Supplementation of spermidine at 40 mg/day has minimal effects on circulating polyamines: An exploratory double-blind randomized controlled trial in older men. Nutr Res, 2024. PMID 39405978
  2. [2]Effects of Spermidine Supplementation on Cognition and Biomarkers in Older Adults With Subjective Cognitive Decline: A Randomized Clinical Trial. JAMA Netw Open, 2022. PMID 35616942
  3. [3]Safety and tolerability of spermidine supplementation in mice and older adults with subjective cognitive decline. Aging (Albany NY), 2018. PMID 29315079
  4. [4]High-Dose Spermidine Supplementation Does Not Increase Spermidine Levels in Blood Plasma and Saliva of Healthy Adults: A Randomized Placebo-Controlled Pharmacokinetic and Metabolomic Study. Nutrients, 2023. PMID 37111071

Spermidine and other dietary supplements are not intended to diagnose, treat, cure or prevent any disease, and these statements have not been evaluated by the FDA. Talk to your clinician or pharmacist before starting a supplement, especially if you take prescription medicines. This page has no product or affiliate links.

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