The answer to “what is a salt form of a drug” is its active molecule paired with an oppositely charged partner. That partner is called a counterion. The pairing can change how easily the drug dissolves, stays stable or can be prepared.

“Free base” and “free acid” name forms without that added salt partner, depending on the molecule's chemistry. Salt names often include sodium, acetate or hydrochloride. They aren't strength ratings, and a longer chemical name doesn't mean a stronger medicine.

What is a salt form of a drug in official terms?

FDA distinguishes the active ingredient from the active moiety, meaning the core responsible for the drug's action. A salt can contain that same core while being a different active ingredient.

FDA's December 2014 explanation defines it: “The active moiety is the molecule or ion responsible for the physiological or pharmacological action of the drug substance.”

Its naming guidance, dated June 2015, explains the United States Pharmacopeia's Salt Policy. USP publishes medicine-quality standards. The policy became effective May 1, 2013, and generally bases a new drug product's name and strength on its active core. Exceptions exist.

That naming policy doesn't make different salts interchangeable. FDA's guidance covers approved prescription drugs and says it “does not address naming and labeling of compounded preparations,” medicines prepared for individual prescriptions. USP's own policy, reprinted in the guidance's appendix, extends the same naming and strength rule to USP monographs for compounded preparations.

Why medicines have salt forms

A useful drug molecule still has to become something that can be made, stored and measured reliably. Salt selection helps address those practical problems. It doesn't establish better results for a patient.

In a 2007 Journal of Medicinal Chemistry analysis, Paulekuhn and colleagues examined FDA's Orange Book, its list of approved drug products. Chloride was the most frequently used negatively charged partner; sodium was most common for salts made from acidic drug molecules. Salt forms are ordinary pharmaceutical chemistry, rather than a special category of peptide treatment.

Semaglutide sodium vs semaglutide base

As of October 29, 2026, the day this article was written, FDA's GLP-1 page carries “Content current as of: 10/01/2026.” GLP-1 is a gut hormone involved in appetite and blood sugar.

The page identifies semaglutide sodium and semaglutide acetate as “different active ingredients” from those in branded medicines. FDA is “not aware of any lawful basis for their use in compounding.” It also says it lacks information establishing that those salts share the branded ingredient's chemical and drug properties.

FDA's semaglutide dosing error alert identifies the base form as the ingredient in branded semaglutide medicines. A familiar first word on a label doesn't settle the full ingredient's identity.

Compounded semaglutide is different from an FDA-approved product such as Ozempic: the compounded formulation is not FDA-approved.

Why the exact form matters in compounding

A bulk drug substance is the starting active ingredient. Section 503A is the federal framework for traditional pharmacy compounding. A USP monograph is an official quality standard for an ingredient.

Under 21 U.S.C. 353a(b)(1)(A), the ingredient routes run in order:

  • If an applicable USP or National Formulary monograph exists, the ingredient must meet it and the USP compounding chapter.
  • Without such a monograph, it must be a component of an approved drug.
  • If neither applies, it must appear on the final 503A bulks list.

A salt that isn't the branded drug's component doesn't inherit that component's position. A similar name isn't a substitute for meeting the ingredient requirement. Other compounding requirements apply too.

Peptide acetate vs free base

Peptides are short chains of amino acids, the building blocks of proteins. Their salt partners matter in the paperwork as well as in the laboratory.

FDA's July 23–24, 2026 briefing materials listed a free-base form and an acetate form separately for each of seven peptides: BPC-157, KPV, TB-500, MOTS-c, emideltide (also called DSIP), Epitalon and Semax. The July peptide review explainer covers that advisory process. BPC-157 is not FDA-approved.

As of October 29, 2026, the day this article was written, HHS's draft policy notice, filed October 28, is public; it is not a final 503A bulks-list rule. HHS says it does not intend to take enforcement action against a state-licensed pharmacy, federal facility or licensed physician compounding with six named peptides when all ten of the policy's conditions are met. Its Appendix B specifies the form of each: the acetate for BPC-157, TB-500, Epitalon, KPV and MOTS-c, and the free base for Semax. The HHS policy explainer explains the conditions.

A licensed provider may still prescribe — that decision is between you and your doctor.

Does the strength mean the core or the whole salt?

The counterion adds weight. So a milligram of the whole salt holds less than a milligram of the active core. FDA's naming guidance generally uses the core amount for covered drug products, while requiring the salt information elsewhere on the label. Exceptions can use salt strength with an equivalency statement explaining the corresponding core amount.

FDA's December 2014 explanation describes medication errors caused by misunderstanding that distinction. USP's policy has labeling give the names and strengths of both the core and the salt; for a compounded prescription, the pharmacy's label or record is where that shows.

Laboratory testing shows why the distinction matters. In Johnson and colleagues' 2015 Journal of Pharmaceutical and Biomedical Analysis study, one laboratory peptide measured 99.5% by a purity test that separates chemical components. Yet its peptide content by weight was 80.3%. Water and a counterion accounted for part of the difference. These were material measurements, not treatment results.

Concentration means drug amount in a given liquid volume. It is a separate question again; syringe units and milligrams explain that distinction.

Mistakes people make with salt names

Reading acetate as contamination. Acetate can be the intended salt partner. Whether a batch meets its specifications, the limits it must satisfy, needs testing.

Reading arginate as better. Another salt name doesn't demonstrate better absorption or outcomes. The BPC-157 arginate comparison addresses that separate question.

Applying one drug's statement to another. FDA's current GLP-1 page discusses both semaglutide and tirzepatide, but its salt-form passage specifically names semaglutide. It doesn't make the same finding about tirzepatide salts. That silence doesn't establish equivalence between any proposed forms.

Through Promise, tirzepatide is dispensed by a licensed U.S. compounding pharmacy. It is different from an FDA-approved product such as Mounjaro: the compounded formulation offered here is not FDA-approved.

A certificate of analysis reports tests for a batch. Bioequivalence compares how two medicines reach the body. Neither term means the same thing as salt identity. The semaglutide ingredient-sourcing explainer covers a different question: where the starting material comes from.

Formulations vary by pharmacy and prescription. The dispensing pharmacy's record identifies the actual ingredient and explains how strength is stated. The prescriber sets the dose.

At Promise, a licensed provider reviews every request, and not everyone qualifies.