MOTS-c side effects

What is known in people

FDA's 2026 review found no clinical studies or human exposure data for MOTS-c by any route, so it concluded that the safety risks in humans are unknown.² It also found no nonclinical toxicity studies, such as repeat-dose, genetic, reproductive or cancer studies.² USADA states that no human clinical trial has been completed and that there are no data on long-term use.¹

So the MOTS-c side effects listed below are not rates from trials. They come from three weaker kinds of evidence: user reports, a trial of a related molecule, and FDA's review of the risks.

At a glance, by seriousness

Reported effects, grouped by source

Unverified reports from people who purchased MOTS-c online

USADA summarizes these effects reported by people who say they purchased MOTS-c online:¹

• Increased heart rate or heart palpitations
• Irritation at the injection site
• Insomnia
• Local or whole-body immune reactions
• Fever

These are anecdotes, not study results.¹ No study has measured how often they occur.²

A company trial of the analog CB4211 (not MOTS-c)

CB4211 is a modified analog of MOTS-c, so its results may not carry over.³ The phase 1a/1b trial enrolled 88 people.⁴

• In the 4-week phase 1b part, injection site reactions were the only adverse events seen in more than 10% of treated participants.³ They were short-lived and generally mild to moderate.³
• The company reported no serious adverse events.³
• In November 2018 the trial was paused to address mild injection site reactions that had become unexpectedly persistent.⁵

Risks FDA has flagged

Immune reactions

FDA is concerned that injected MOTS-c may trigger an immune response, because the peptide may form aggregates and may carry peptide-related impurities.² Such responses can range from antibodies with no symptoms to life-threatening reactions.² Antibodies could in theory also neutralize the body's own MOTS-c.² FDA's list of bulk substances that may present significant safety risks names immunogenicity, impurities and characterization problems for MOTS-c.⁶

Identity and quality

FDA considers MOTS-c free base not well characterized.² The free base and the acetate salt are different ingredients, and naming that does not follow chemical standards can mean a person receives a different substance than intended.² Peptides can also clump or degrade with changes in pH, heat, concentration or impurities.²

Unknown organ effects

FDA reviewers say the molecular targets of MOTS-c are unknown, which makes it hard to predict which organs it may affect.² With no toxicity studies on record, no source describes effects on specific organs at any exposure.²

Why no reports does not mean safe

FDA's adverse event database had no MOTS-c reports in searches through March 9, 2025.² That absence says little, because compounders generally do not report adverse events to FDA.² There are also no data on use in pregnancy, in children or alongside other drugs, since FDA found no human exposure data and no reproductive toxicity studies.²

Warnings

• Sport. MOTS-c is prohibited at all times under section 4.4.1 (activators of AMPK) of the World Anti-Doping Agency Prohibited List.¹ USADA says a therapeutic use exemption is highly unlikely because it has no approved therapeutic use.¹
• Long-term use. No data exist on what happens with long-term use.¹
• Approved options. FDA's advisory committee reviewed MOTS-c for obesity and osteoporosis, conditions for which FDA-approved medicines already exist.⁷²
• General practice. For handling and safety basics that apply to any peptide, see Peptide safety basics.

Related pages

• What is MOTS-c? for the full profile
• MOTS-c dosage for the doses used in studies
• MOTS-c benefits and uses for what the studies found