By Dr. Harriet Kamendi, PhD – Regulatory Toxicologist & CEO, Kandih BioScience

 A Signal Too Big to Ignore

In November 2025, the American Heart Association (AHA) reported early findings linking long-term melatonin use (≥1 year) with alarming outcomes:

~90% higher risk of heart failure

~2× higher all-cause mortality

~3.5× higher risk of hospitalization for heart failure

(AHA, 2025
, Science Media Centre Spain, 2025
)

For professionals in toxicology, regulatory science, or product development, this should be a red flag:

 Just because something’s natural doesn’t mean long-term exposure is safe.

The one clear idea: Toxicity is a function of dose, duration, and context.
And for melatonin, duration just entered the risk equation.

 Why Melatonin’s Long-Term Use Raises Toxicology Questions
1. Hormonal Modulation = Biological Exposure

Melatonin isn’t a vitamin — it’s a hormone that regulates circadian rhythm.
Taking it nightly alters neuroendocrine signaling, sleep-wake regulation, and potentially metabolic and cardiovascular function.

In other words, you’re not just supplementing — you’re modulating a biological system.
Chronic modulation can lead to compensatory changes, desensitization, or unintended effects on cardiac rhythm and vascular tone.

2. Duration-Dependent Toxicity

Most toxicology models focus on acute or short-term exposure. But melatonin is often used daily for years, creating a chronic exposure scenario.

The AHA data suggest that even low nightly doses may accumulate risk over time through subtle hormonal and metabolic effects.

For toxicologists, this reframes melatonin from a benign supplement to a dose-duration continuum of risk — especially in aging or cardiovascularly compromised users.

3. Regulatory Toxicology Weakness in Supplements

In the U.S., melatonin is marketed as a dietary supplement, not a drug.
That means:

No required pre-market approval

No mandatory long-term toxicology studies

No structured post-market surveillance

(FDA – Dietary Supplement Regulatory Framework
)

This gap leaves millions of consumers exposed without robust lifecycle safety data.
The AHA findings highlight the flaw in assuming that “over-the-counter” equals “long-term safe.”

4. Product Development Implications

Manufacturers have a responsibility to design products that remain safe over years of use — not just during a 12-week trial.

That means integrating pharmaceutical-grade design controls into supplement development:

Establishing impurity limits and stability toxicology

Evaluating excipients and bioavailability modifiers

Including cardiovascular and endocrine endpoints in long-term models

Ensuring accurate labeling about duration of use and risk populations

Long-term use demands drug-level thinking, even in a supplement market.

 Tactical Takeaways for Toxicologists & Developers

 1. Initiate Long-Term Exposure Studies

Model chronic-use toxicology with endpoints covering cardiovascular, metabolic, endocrine, and neurocognitive domains.
Even low-dose nightly exposure can create cumulative effects.

 2. Reassess “Safe” Levels Over Time

Evaluate dose equivalence for chronic nightly use in different age groups.
Account for altered physiology — aging, comorbidities, and polypharmacy interactions.

 3. Prioritize Cross-Disciplinary Design Reviews

Integrate toxicologists, regulatory strategists, and formulators early.
Map exposure scenarios (e.g., nightly use for decades) to real-world physiology.

 4. Establish Active Post-Market Surveillance

Develop internal safety-monitoring frameworks to track adverse events, consumer feedback, and signal detection.
Supplements need pharmacovigilance, even without an FDA mandate.

 5. Prepare Regulatory Strategies Early

If developing high-dose melatonin for insomnia, engage FDA nonclinical guidance at concept stage.
Retrofitting safety data later is slower, costlier, and reputationally risky.

 My Take: The “Safe Supplement” Myth Needs Retiring

As a regulatory toxicologist, I believe melatonin represents the next big reckoning for supplement safety.
The industry has treated it too casually — assuming minimal toxicity because short-term trials look clean.

But hormones are not inert.
When you take a hormone every night for years, you alter systems that regulate everything from heart function to glucose metabolism.

It’s time to flip the paradigm:

 Supplements that act like drugs should be treated like drugs until proven otherwise.

Companies that build lifecycle toxicology into product design — rather than retrofitting safety later — will not only protect consumers but also their own brands.

 The Bottom Line

“Natural” ≠ “Risk-Free.”
When a supplement modulates a hormone, the rules of toxicology apply.

For toxicologists, regulators, and product developers, the message is simple:

 Design for duration, not just dose.
Build safety in — from formulation to post-market.

Because in the end, it’s not the short-term trials that reveal toxicity — it’s time.

 References

1. American Heart Association (AHA). Long-term use of melatonin supplements to support sleep may have negative health effects. News release, Nov 3, 2025. https://newsroom.heart.org/news/long-term-use-of-melatonin-supplements-to-support-sleep-may-have-negative-health-effects

2. Science Media Centre Spain. Continued use of melatonin for insomnia is associated with increased risk of heart failure. Nov 3, 2025. https://sciencemediacentre.es/en/continued-use-melatonin-insomnia-associated-increased-risk-heart-failure

3. U.S. Food and Drug Administration (FDA). Dietary Supplement Regulatory Framework. https://www.fda.gov/food/dietary-supplements

4. Centers for Disease Control and Prevention (CDC). Sleep and Cardiovascular Disease Risk. https://www.cdc.gov/heart-disease/about/sleep-and-heart-health.html

5. Matthew S, et al. Melatonin in Sleep Disorders: A Systematic Review and Meta-analysis. 2025. https://www.sciencedirect.com/science/article/pii/S0149763422002123