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Mitochondria-targeted tetrapeptide · safety

SS-31 side effects

Also written SS31.

The ss-31 side effects reported most often are injection-site redness, injection-site pain and injection-site hardening. The full list is below, with the FDA label cited at the bottom of the page.

Rarer, but worth being able to spot: serious allergic reactions.

The sources describe these effects in relation to the dose and to the early weeks.

SS-31 is a peptide four amino acids long. It gathers inside mitochondria, the parts of a cell that make energy, and sticks to a fat there. It is sold online for energy, mitochondrial health and slower aging.

The same molecule is an approved medicine for a rare inherited condition, at 40 mg a day under the skin. It was tested for the reason people buy it. In 41 older adults with failing mitochondria, it moved energy production about as much as placebo. The vials sold for that use hold 5 mg, an eighth of one day.

Also sold as Forzinity — one molecule, so these reactions apply to every brand of it.

Further down: the full list with frequencies · when to get medical help · questions

Medically reviewed by Jennifer Montecillo, MD · non-practicing medical reviewerReviewed 2026-08-13open the primary sources

At a glance

Common reactions listed

4

Serious reactions listed

1

Boxed warning

None on label

Strongest source

FDA label

The counts show how many distinct reactions the FDA label names. The percentages show how often a reaction appeared in a study group, not the chance that it will happen to you.

Common reactions

The full list, with the frequency band the FDA label gives for each one.

Common reactionslabel frequency
ReactionFrequency
Injection-site rednessEvery participant on the drug in the 12-person trial, against a quarter of those on placebo
Injection-site painThree quarters of participants on the drug, against two fifths on placebo
Injection-site hardeningTwo thirds of participants on the drug, against a sixth on placebo
Raised eosinophils, a white blood cellFrequent; it peaked around 90 days and returned to where it started over 6 to 12 months

Serious reactions to watch for

These are rarer, and they are the ones clinicians monitor for. Seek medical care if you have symptoms.

Serious — monitorwarning/precaution
ReactionFrequency
Serious allergic reactionsSerious — monitor. The label describes reactions needing emergency treatment. These have begun from minutes to months after the first dose

FDA labelEvery reaction above comes from the product’s regulatory document. These are label facts, not personal advice.

When to seek medical care

Each one below is a serious reaction from the table above, written as the signs you would actually notice. Spotting them is the job of this section; working out what they mean is a clinician’s.

Severe hypersensitivity reaction

Urgent

Signs: Swelling of the face, lips, tongue or throat, trouble breathing or swallowing, a rash or hives spreading fast, or suddenly feeling faint.

This is the one on the list that does not wait. Call emergency services immediately rather than a clinic.

EmergencySome symptoms should not wait for an appointment. Call emergency services (911 in the US) if they are severe, getting worse fast, or involve trouble breathing, chest pain, fainting or confusion.

2Read deeperTiming, evidence limits, and product context

When these effects tend to occur

The cited evidence describes these effects in relation to the dose and to the early period of taking it, rather than as a constant background throughout.

When a study reports how side effects changed over time, it describes the group as a whole. It cannot predict one person’s experience.

Forzinity side effects

Forzinity is a brand name for ss-31. The frequency bands above describe the molecule. Percentages can still differ by brand because each label may be based on different trials, doses and groups of people.

Forzinity holds an accelerated approval.

FDA grants those on a marker rather than on how people function, and the marker here was knee extensor strength. Whether the approval stands depends on a confirmatory trial that has not reported. The approval covers Barth syndrome in people weighing at least 30 kg, and nothing else.

Material sold online as SS-31 is not that product. Forzinity is a ready-to-use solution at 80 mg per mL. The research vials hold a powder to be mixed, and no regulator has examined what is in them.

Common questions

How long do ss-31 side effects last, and do they go away?

The sources do not commit to a set number of days. What they describe is a pattern — reactions cluster after you start and after each increase, then ease while the dose is held steady. Any page quoting an exact number of days is quoting something the sources do not say.

What are the most common ss-31 side effects?

Injection-site redness, injection-site pain, injection-site hardening and raised eosinophils, a white blood cell — the table above has the rest, each with its frequency band and source.

Does ss-31 have a boxed warning?

No — its label carries none. That reflects what regulatory review has and has not covered, not a finding that serious risks were looked for and ruled out.

Can the ss-31 dose be lowered if side effects are hard to tolerate?

That decision belongs to the prescribing clinician. The label sets a single dose rather than a ladder, so there is no step to hold at. Any change to it sits with the prescriber.

Does ss-31 cause hair loss?

Hair loss is not among the reactions listed on this page for ss-31, because the FDA label cited here does not carry it. Anything missing from the tables is outside what can be sourced here rather than ruled out, and a symptom that worries you belongs with a clinician.

Is fatigue a listed ss-31 side effect?

No — the FDA label cited here does not list it. That describes what was reported, not proof that the symptom cannot happen.

Is constipation a listed ss-31 side effect?

Not separately. If a source groups stomach and gut events together, this page keeps that group intact. It does not invent named reactions the source never listed.

What should someone do about a serious ss-31 reaction?

Contact a clinician promptly, and emergency services if symptoms are severe or getting worse quickly. The section above describes what those reactions actually look like, so they can be spotted early rather than explained away.

Do the frequencies on this page mean the chance it happens to one person?

No. These figures describe groups in a study. A band shows how often a reaction appeared under that trial’s conditions. It cannot predict what will happen to one person.

Related

The schedule these reactions were recorded against, the comparisons, and the sourcing rules behind every grade on this page.

1primary source, each with the day we read it — open the documents used on this page