While composing this article, I endeavoured to ensure that no form of bias interfered with my reasoning, research, and interpretation of the findings. At Jotunheim Nutrition, we offer products containing Stevia for various reasons, primarily because we heed our customers’ requests for a sweetness level in certain products that would otherwise be less palatable. Additionally, my research has led me to conclude that Stevia represents the least harmful category of sweetener currently available, particularly since monk fruit is prohibited in Sweden.

Allow me to conduct a comprehensive examination of Stevia research. This article is grounded in factual information, and I will strive to provide credible sources whenever feasible and necessary. For those who prioritise scientific opinions, particularly if you have been influenced by wellness content creators asserting that Stevia is detrimental based on scientific studies, it is imperative to scrutinise the actual findings within these studies. It is contradictory to proclaim a distrust in science while simultaneously relying on outdated, incomplete, or erroneous scientific methods and research to support one’s beliefs. Let us commence.

Stevia AND Fertility: What the Science Shows (Humans first)

What we know (AND NOT) in HUMANS

• Direct human fertility trials are basically absent. No randomised controlled trials (RCTs) have tested stevia for effects on time-to-pregnancy, ovulation, semen quality, or pregnancy outcomes. Major safety reviews (EFSA/JECFA/FDA) conclude steviol glycosides are safe at current intake levels and not linked to reproductive toxicity based on the overall toxicology package (largely animal data). European Food Safety Authority+2European Food Safety Authority+2
• One 2025 cross-sectional study in men (n=80, Iraq) compared stevia consumers vs non-consumers: no change in testosterone or sperm motility, but lower sperm count and a small, non-significant rise in abnormal morphology in the stevia group. Observational design → can’t prove causation; diet/lifestyle confounders possible. (Still, it’s the first human signal worth noting.) pharmakeftiki.hsmc.gr
• In-vitro (lab) human sperm study (2016): exposing human sperm to steviol increased progesterone production in the assay; authors flagged a theoretical endocrine-disruption potential that needs in-vivo confirmation. This is not evidence of harm in people but a mechanistic clue. PubMed
  

High-quality human evidence linking stevia (purified steviol glycosides) to impaired fertility is very limited. One small observational study suggests a possible association with lower sperm count; confirmatory studies are needed. Regulatory bodies still consider stevia safe within the ADI and not associated with reproductive toxicity based on the full dataset. European Food Safety Authority+1

What we know from ANIMALS / CELLS

The study that everyone refers to when mentioning ”Stevia is bad for fertility”:

The 1968 rat decoction study

…Using whole-leaf water tea, not purified glycosides) reported reduced fertility in female rats, with effects persisting after stopping. Methods/dosing differ greatly from modern food use. PubMed

Let us break it down:

What they did:

• Researchers in Paraguay in 1968 gave female rats a water decoction of dried Stevia rebaudiana leaves (essentially a strong tea, not isolated steviol glycosides).
• Dosing was very high: the equivalent of several grams of leaf material per kg body weight daily — far above anything comparable to human sweetener intake.
• The rats were exposed for a prolonged period before and during mating.

What they found:

• Female rats consuming the leaf tea had reduced fertility and lower pregnancy rates compared with controls.
• Some reports describe failure to conceive or decreased numbers of implantation sites.
• The effect allegedly persisted for up to two months after discontinuation of the extract — suggesting a lasting influence on reproductive physiology.

Major limitations ON THE STUDY EVERYONE LINKS STEVIA WITH ”POOR FERTILITY OUTCOMES”

1. Crude extract
   • It used whole-leaf decoctions, not purified steviol glycosides (Rebaudioside A, Stevioside, etc.) that are approved for food use today.
   • The leaves contain other phytochemicals (e.g. diterpenes, essential oils, tannins, chlorogenic acids) that could cause unrelated pharmacologic effects at high doses.
2. Non-standardised preparation
   • No chemical characterisation or measurement of dose by steviol equivalents.
   • Unknown concentrations; boiling may have concentrated non-sweet compounds.
3. Extremely high dosing
   • Likely many hundreds of times higher than any realistic human intake.
   • Modern safety studies typically use ≤2 000 mg/kg body weight/day of purified steviol glycosides — with no reproductive toxicity observed.
4. Small sample size, incomplete reporting
   • Original data tables were never fully published in a peer-reviewed journal; subsequent references come from secondary citations (Melis, 1999; EFSA summary).
   • No proper control for nutritional or stress effects.
5. Not reproduced
   • Later independent groups (Yodyingyuad & Bunyawong, 1991; Medon et al., 1982; Oliveira-Filho et al., 1989) performed multi-generation reproductive studies with purified stevioside or whole-leaf powder and found no impairment of fertility or fetal development, even at very high doses.
     

Despite its methodological flaws, the 1968 finding circulated for decades, largely through alternative-medicine and early toxicology discussions, creating the persistent “stevia causes infertility” myth. It remains a cautionary example of how poorly controlled early studies can shape public perception long after being scientifically resolved.

This exact study also gave birth to the thought that Stevia was somehow used as contraceptive by tribes in South America.

myth: tribes IN SOUTH AMERICA USED STEVIA AS CONTRACEPTIVE

Indigenous Guaraní people of Paraguay and Brazil have used Stevia rebaudiana leaves for centuries as a sweetener and herbal tea (“ka’a he’ê” literally means “sweet herb”).

Early ethnobotanical descriptions (e.g., by Moisés Santiago Bertoni, 1899–1905) list its use for sweetening maté, for stomach comfort, and diuretic or tonic purposes, NOT contraception.

No pre-20th-century Guaraní or Paraguayan records mention fertility control.

Researchers speculated that the finding of reduced rat fertility might reflect a traditional use they had “heard of” — but no primary source or indigenous account was ever cited.

Later English-language reviews repeated the speculation, and it snowballed into “folk contraceptive” statements in popular herb encyclopaedias and websites.

This gave birth to the Ehrlich reference in In Population, Resources, Environment: Issues in Human Ecology
by Paul R. Ehrlich and Anne H. Ehrlich (first edition 1970, later updated editions), the authors wrote something to the effect of:

“The Guaraní Indians of Paraguay are said to use an infusion of the leaves of Stevia rebaudiana as a contraceptive.”

That single sentence (or close variations of it) appears in various editions and was later cited by numerous secondary sources — including herbal compendia and safety assessments (e.g. EFSA’s 1999 dossier mentions it).

The issue with this reference is:

• No primary ethnographic source (Guaraní oral record, field ethnobotany report, or pharmacological investigation) was ever cited by the Ehrlichs.

• Scholars who later tried to trace the statement (for example, Curi et al., J. Ethnopharmacol. 1986; Geuns 2003, Phytochemistry) found no verifiable original reference describing such use among the Guaraní.

• It appears that Ehrlich and Ehrlich reported a rumour or hearsay from secondary anthropological notes circulating at the time, not firsthand documentation.

• Later writers (including the 1968 rat study by Melis and others in the 1980s) retroactively linked their animal findings to this old folkloric remark — reinforcing the myth without ever proving it ethnographically.

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Other animal studies:

• Multigeneration & reproduction studies (modern toxicology): generally no reproductive/developmental toxicity for approved steviol glycosides at very high doses; these studies underlie today’s ADI. ScienceDirect+1
• Newer animal signals: A 2025 rat study found early-life stevia exposure reduced pregnancy rates and litter size and prolonged gestation; relevance to typical human consumption is unclear and needs human follow-up. Other rodent work in metabolic-disease models reports neutral or even protective testicular effects. Animal findings are mixed and dose/form dependent. jn.nutrition.org+1

THE BIG QUESTION: Has stevia been tested in humans for fertility?

No. Not in robust intervention trials. Safety authorities rely on comprehensive toxicology (mostly animal multi-generation studies) and human exposure assessments; fertility-specific human RCTs are lacking. The first human observational paper (2025) reports lower sperm counts in users—hypothesis-generating, not definitive. pharmakeftiki.hsmc.gr

WHAT SIGNIFICANCE DOES IT HOLD THAT THESE STUDIES ARE CONDUCTED ON RATS RATHER THAN HUMANS? WHAT ARE THE IMPLICATIONS AND RESEARCH OUTCOMES?

1. Hormone regulation:
   Rats, mice, and humans all have oestrogen, progesterone, FSH, and LH — but their feedback loops and receptor sensitivities differ dramatically.

• Rats, for instance, have 4–5 day estrous cycles, not monthly ovulatory cycles like humans.
• A compound that subtly affects rat ovarian function could have no measurable effect on the human menstrual cycle.

2. Metabolism of compounds:
Steviol glycosides are converted in the gut by microbial hydrolysis into steviol, which is then glucuronidated and excreted.
The gut microbiota composition, intestinal transit time, and enzyme activity differ hugely between species.

A dose that overwhelms a rat’s detox system might be fully processed and harmless in humans (or vice versa).

3. Dose scaling:
Toxicology studies often use doses hundreds or thousands of times higher than realistic human exposure. Scaling by body weight alone doesn’t perfectly model pharmacokinetics or chronic intake.

Something else we need to address is what human fertility involves:

Nutritional status, metabolic health, endocrine feedback, emotional stress, circadian rhythm, and immune function, all intertwined.
Animal labs can’t model these holistic interactions.

For example, if a human’s fertility changes after switching to stevia, the cause could be weight loss, blood sugar improvement, or other lifestyle shifts — not a direct gonadal effect of the molecule itself.

That’s why controlled human studies (RCTs) are essential for causality.

aND THEREFORE, ALL STUDIES DONE ON RATS REGARDING STEVIA:

• Are hypothesis-generating, not definitive.

• They must be interpreted as possible mechanisms to investigate in humans, not proof of effect.
• Regulatory agencies (EFSA, FDA, WHO/JECFA) require multiple species, multiple generations, and no observed effects at high doses before approving — which steviol glycosides have passed.
• However, absence of human fertility trials means there’s still uncertainty — we can’t rule out subtle effects that only occur in human endocrine systems.

Sources YOU MIGHT WANT TO CHECK

• EFSA Scientific Opinion (2010): steviol glycosides not genotoxic/carcinogenic; no reproductive toxicity identified; ADI 4 mg/kg bw/day (as steviol equivalents). European Food Safety Authority+1
• EFSA updates (2023–2024): ADI reaffirmed; includes newer production methods (fermentation/enzyme-modified glycosides). PMC+1
• FDA GRAS notices (2018–2023): intake assessments below ADI; supports safety of high-purity steviol glycosides. U.S. Food and Drug Administration+1
• Human observational study (2025): stevia intake vs semen parameters (no T change; lower sperm count). pharmakeftiki.hsmc.gr
• In-vitro human sperm study (2016): steviol ↑ progesterone production (mechanistic signal). PubMed
• Animal classics: 1968 rat decoction study (reduced fertility); 1991 hamster study (no adverse effects on growth/reproduction at high stevioside doses); multi-generation toxicology (no repro toxicity at NOAELs used to set ADI); 2025 early-life rat exposure showing adverse outcomes. jn.nutrition.org+3PubMed+3PubMed+3
• Narrative/umbrella reviews on NNS & fertility: context on non-nutritive sweeteners and reproductive outcomes. Cambridge University Press & Assessment

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MY ADVICE FOR PROFESSIONALS AND WELLNESS COACHES

I recommend that if you are a reputable practitioner, a wellness content creator, or a health coach, you should verify the actual facts before making significant claims such as “Stevia harms your fertility” to avoid being perceived as unprofessional.