Peptide Therapy · Reviewed by Ian K. Tseng, MD

Topical vs. Injectable Peptides: What's the Difference?

One of the most common questions online is some version of: "Why are people injecting peptides — can't you just use a serum?" It is a good question, and the answer explains the entire line between cosmetic skincare and medical care. The delivery method is not a detail. It is the difference.

Published July 8, 2026 · Medical review by Ian K. Tseng, MD, Medical Director

First, if you haven't already

If you are still fuzzy on what a peptide even is, start with our plain-English guide to peptides. The one-line version: a peptide is a short chain of amino acids that acts as a signaling molecule, telling your cells what to do.

Topical peptides: cosmetics that work at the surface

Topical peptides are ingredients formulated into creams, serums, and eye products. Two you will see named on labels are copper peptides (GHK-Cu) and Matrixyl, both marketed to support the skin's own collagen and elastin. Because they sit in the cosmetic category, they are sold over the counter, do not require a prescription, and make appearance-based claims rather than medical ones.

Research suggests some of these ingredients may improve the look of fine lines, skin texture, and firmness with consistent use — but their reach is limited to the skin's surface and upper layers, which is exactly what a cosmetic is supposed to do. How much any given serum does depends on the specific peptide, its concentration, the formulation, and your individual skin. A good serum is a reasonable part of a skincare routine. It is not a medical treatment, and it cannot do what an in-office procedure like Morpheus8 RF microneedling or a systemic therapy does.

Why some peptides can't just be a cream or a pill

Here is the biology that drives everyone toward injections. Peptides are fragile. Many are too large to pass through the skin barrier in a meaningful amount, and many are broken down by digestion before they can be absorbed if swallowed. So for a systemic peptide to reach the tissues where it acts, in the amount it needs to act, it generally has to bypass the skin and the gut — which in practice means injection.

That is why you see the injections. It is not that injecting is trendy; it is that, for these molecules, a cream or a capsule would not deliver an intact, useful dose. And the moment something is entering your bloodstream, the safety bar rises sharply — which is the whole reason systemic peptides belong inside medical supervision.

Injectable / systemic peptides: a medical program, not a purchase

Our physician-supervised peptide therapy is a medical service. A licensed physician reviews your goals, health history, and bloodwork through a Good Faith Exam, and only then decides whether a prescribed protocol is appropriate. The programs are described by categories of care — aesthetics and anti-aging, recovery and tissue repair, metabolic optimization, and performance and vitality — organized around what they support in the body rather than around product names. Which therapy, if any, fits you is a clinical decision, and not everyone qualifies.

This is the opposite of buying a serum. There is an exam, there is bloodwork, there is a physician taking responsibility for what enters your body. Our companion piece on why peptide therapy starts with bloodwork walks through the labs a physician reviews first.

The comparison at a glance

The one thing not to do

Do not buy injectable peptides from an unregulated online seller. When you order a vial from an unknown vendor, nothing about its purity, dose, sterility, or even its actual contents is verified — and no physician has evaluated whether it is safe or appropriate for you. This is not hypothetical: in 2023 the FDA banned copper peptide injections after finding impurities that triggered immune reactions in some people, even though copper peptides are perfectly common in topical products. The delivery method changed the risk entirely. We go deeper on this in Are peptides safe?

Frequently asked questions

This article is educational and is not medical advice. Statements have not been evaluated by the FDA. Peptide therapy is a physician-supervised medical service; specific protocols are determined individually after a Good Faith Examination and bloodwork, and not all applicants qualify. Some compounded medications used in physician-prescribed protocols are not FDA-approved. Data from clinical trials on FDA-approved medications should not be used to make assessments related to compounded medications. Soothe IV's peptide program is available in California.