Why some drug names carry a salt, from hydrochloride to hyclate

Search FDA's Orange Book for metoprolol and two separate ingredients come back. Metoprolol tartrate tablets list strengths such as "50MG." Extended-release metoprolol succinate tablets list theirs as "EQ 50MG TARTRATE," meaning each tablet holds as much metoprolol as 50 mg of the other salt. All 17 active listings for that succinate strength use the same wording, according to GxRadar's review of FDA's Orange Book data files¹ as published in October 2026.

The word after a drug's name, whether succinate, tartrate, hydrochloride or hyclate, identifies the salt the active molecule is made as. On some labels it is part of the official name; on others it appears only in the fine print. That choice follows a naming policy the U.S. Pharmacopeia adopted in 2013 and FDA wrote into guidance in 2015, and it affects more than spelling, because FDA treats different salts of the same molecule as different active ingredients. This explainer covers how salts are named, how strength is stated, and what the difference means for substitution and price.

Salt, base and active moiety

Many drug molecules are manufactured bound to an acid or a base, forming a salt. Federal rules separate the two parts. The "active moiety" is the molecule or ion responsible for the drug's action, "excluding those appended portions of the molecule that cause the drug to be an ester, salt," or other noncovalent derivative, under 21 CFR 314.3². In USP's words, the active moiety of a hydrochloride salt of a base "is the free base," as reprinted in FDA's 2015 guidance³.

The active ingredient is the whole salt. Sertraline hydrochloride, amlodipine besylate and losartan potassium are each one active moiety paired with a different counter-ion. Water bound into a crystal is a different matter. Anhydrous and hydrated forms, and different crystal forms called polymorphs, "are considered to be the same active ingredient," the Orange Book preface⁴ says, consistent with the Orange Book filing doxycycline monohydrate products under plain "doxycycline" while listing doxycycline hyclate, a salt, as a separate ingredient.

How the strength is written

For many salts the Orange Book states strength in terms of the active moiety, marked "EQ" for equivalent. The designation is "generally used in connection with salt drug products to indicate that the strength of such drug product is being expressed in terms of the equivalent strength of the active moiety (e.g., 'EQ 200 MG BASE')," the preface explains⁴. Older products follow no single rule. The federal price survey that pharmacies report to, CMS's National Average Drug Acquisition Cost⁵ file, is not consistent either: it writes some names with the salt and drops it from others.

Orange Book entries come from FDA's October 2026 data files¹; NADAC descriptions come from the CMS file dated Nov. 4, 2026⁵. GxRadar's drug pages for sertraline, atorvastatin and losartan track the same NADAC rows.

The 2013 USP policy and FDA's 2015 guidance

USP announced its salt naming policy in a Nov. 19, 2012 press release and set May 1, 2013, as the start date, RAPS reported at the time⁶. FDA issued a draft guidance on applying it in the Federal Register on Dec. 26, 2013⁷ and finalized the guidance in June 2015⁸. A USP monograph title usually becomes a new product's established name, the guidance notes³, so the policy reaches labels directly.

Under the policy, as FDA summarizes it in the final guidance³, a new drug product made with a salt is named for the active moiety ("newdrug tablets" instead of "newdrug hydrochloride tablets"), and its strength is stated in terms of the active moiety as well. The full salt name and strength must still appear elsewhere on the label, usually in an equivalency statement. FDA's sample label lists New Drug 10 mg, followed by "(equivalent to 10.5 mg New Drug Hydrochloride USP)." FDA says matching the name to the basis of the strength should help avoid medication errors caused by a mismatch, such as a name that includes the salt next to a strength based on the moiety.

Exceptions keep the salt in the name when it carries clinical information. FDA's list includes simple salts where the whole salt matters therapeutically, such as lithium carbonate, iron salts, calcium salts, potassium chloride and magnesium sulfate, and cases where the salt changes how the drug is absorbed, distributed, metabolized or excreted in ways that affect a clinician's choice. A product that does not follow the policy risks being misbranded, the guidance warns³; federal law defines a drug's established name as its official name or, if there is none, its title in an official compendium such as the USP, under 21 U.S.C. 352(e)(3)⁹. The policy covers prescription drugs approved under section 505 of the Food, Drug, and Cosmetic Act; it does not address nonprescription products or licensed biologics.

It also looks forward only. USP did not plan to change existing monograph titles unless needed for safety, the guidance says³, which is why many long-established generics still carry the salt in their names.

Why the salt matters for substitution

Naming policy does not change the law on equivalence. "Different salts, esters or other noncovalent derivatives" of the same active moiety "are regarded as different active ingredients," and products containing them are pharmaceutical alternatives that "are not therapeutically equivalent," the Orange Book preface⁴ says. Its examples include tetracycline hydrochloride versus tetracycline phosphate complex capsules. Extended-release and immediate-release versions of the same ingredient are also pharmaceutical alternatives. FDA's salt guidance³ adds that a generic applicant must still show it has the same active ingredient, salt included, as its reference drug, and that the Orange Book will keep listing products by active ingredient.

So metoprolol succinate extended-release tablets and metoprolol tartrate tablets are two different products in FDA's eyes on two counts, salt and release mechanism. Doxycycline hyclate and doxycycline monohydrate capsules are different on one. Because the Orange Book does not rate either pair equivalent, a swap between them falls outside routine generic substitution in states that tie substitution to FDA ratings; GxRadar's explainer on generic substitution and therapeutic interchange describes what that takes, and the guide to extended-release and immediate-release pills covers the release question. Whether two forms of a medicine can be exchanged for a particular patient is a question for a pharmacist or prescriber.

What pharmacies pay for two salt pairs

Different salts also carry different prices. The figures below are NADAC rates, the average acquisition cost pharmacies reported paying, effective Oct. 21, 2026, in the CMS file dated Nov. 4, 2026. They are not what a customer pays at the counter. Each is shown for a 30-count fill, next to the per-unit rate it is computed from.

Thirty monohydrate capsules cost pharmacies about twice what 30 hyclate capsules did, and the extended-release succinate tablets cost about 2.4 times the tartrate tablets, according to CMS NADAC data⁵. The metoprolol gap reflects the release mechanism as well as the salt. Price histories for both forms are on GxRadar's pages for metoprolol succinate ER, metoprolol tartrate and doxycycline hyclate, and the price tracker covers the rest of the basket.

A label's salt word is fixed when the product's name is fixed, and for products named before May 2013 it is unlikely to move. FDA and USP agreed to coordinate any retroactive name change and to make one only for safety reasons, the 2015 guidance says.