By Mitul Agarwal, B.Pharm, MBA. Published October 2026.
"Hydrochloride", often shortened to HCl on a pack, tells you that the medicine's active molecule has been combined with hydrochloric acid to form a salt. The salt is usually easier to dissolve, purify and make into a stable tablet or injection than the molecule on its own. Once it dissolves in the body, the salt and the free base deliver exactly the same active molecule. The only real difference is weight: 500 mg of metformin hydrochloride contains about 390 mg of metformin itself.
For a patient, that is usually the end of the story. For anyone buying, registering or formulating a medicine, it is the beginning of one. The word on the label decides how the API is specified, how quotes should be compared, which regulatory documents apply and whether a "cheaper equivalent" is really equivalent at all.
Why so many medicines are sold as salts
A large number of drug molecules are weak bases. In their pure form, which chemists call the free base, they can be oily, unstable, slow to dissolve in water or simply awkward to crystallise. React the base with an acid and you get a salt: usually a well-behaved crystalline powder with more predictable properties. When the acid is hydrochloric acid, the salt is a hydrochloride.
It is by far the most widely used salt for basic drugs, which is why the word turns up on so many familiar labels: metformin hydrochloride, sertraline hydrochloride, ciprofloxacin hydrochloride, ondansetron hydrochloride. Some molecules pair with two molecules of acid and become a dihydrochloride, as cetirizine does.
It is worth saying plainly that the hydrochloride part is not a second medicine. Chloride is a small, everyday ion. The therapeutic effect comes from what regulators call the active moiety, the part of the molecule that is identical whether it arrives as a salt or as the base.
Manufacturers choose a salt for practical reasons. It tends to dissolve faster, which helps a tablet release its drug consistently from batch to batch. It often keeps better in storage than an oily or easily oxidised base. A free-flowing crystalline powder is easier to purify, mill, blend and compress. And for injections, a water-soluble salt is often what makes a solution possible in the first place. The choice is made early in development and then locked in, because changing it later means new data and, in most markets, a new or varied registration.
Hydrochloride is not the only salt
Basic drugs are also sold as hydrobromides, sulfates, phosphates, mesylates, maleates, fumarates, tartrates, besilates and citrates. Amlodipine besilate and imatinib mesylate are two that most pharmacists will recognise. Acidic drugs go the other way and are paired with metals, which gives us atorvastatin calcium, diclofenac sodium and losartan potassium.
There is one more layer that catches people out. The crystal can also hold water. Ciprofloxacin hydrochloride monohydrate does not weigh the same as anhydrous ciprofloxacin hydrochloride, so a specification has to say which of the two it means.
The arithmetic: salt versus base
Because a salt carries the weight of its acid, a gram of salt contains less active moiety than a gram of base. Converting between the two is a simple ratio of molecular weights:
weight of salt = weight of base × (molecular weight of salt ÷ molecular weight of base)
A few everyday examples show how much the numbers move:
| Product as labelled | Salt form | Equivalent amount |
|---|---|---|
| Metformin hydrochloride 500 mg | Hydrochloride | contains about 390 mg metformin base |
| Amlodipine 5 mg tablets | Besilate | made with about 6.9 mg amlodipine besilate |
| Ciprofloxacin 500 mg tablets | Hydrochloride monohydrate | made with about 582 mg ciprofloxacin hydrochloride monohydrate |
| Sertraline 50 mg tablets | Hydrochloride | made with about 56 mg sertraline hydrochloride |
These figures are rounded and worked out from standard molecular weights. For real formulation work, always use the numbers in the manufacturer's specification and the approved product information.
Labels add a further complication, because they do not all follow the same convention. Some state the strength as the salt ("metformin hydrochloride 500 mg"). Others state it as the active moiety and name the salt in brackets ("amlodipine 5 mg, as besilate"). Which approach a product uses depends on the market and on when it was first approved. Before you compare two products, check which number you are actually looking at.
What this means when you buy an API
In practice, most costly misunderstandings about salts come down to five things.
The exact form has to be in the RFQ. "Ciprofloxacin" is not a specification. Ask for "ciprofloxacin hydrochloride monohydrate, USP" or "ciprofloxacin base, EP", whichever your dossier is built on. Our RFQ checklist covers the other details suppliers need to quote properly.
Prices have to be compared on the same basis. A price per kilogram of salt and a price per kilogram of base are not the same thing. Convert both to cost per kilogram of active moiety before deciding which offer is cheaper.
The assay basis on the CoA matters. Assay may be reported on the dried basis, on the anhydrous basis or "as is". Your batch formula has to use the same basis as the pharmacopoeia monograph you follow.
The documents must cover that exact salt. A DMF, CEP or ASMF is filed for one specific substance. A CEP for the hydrochloride does not cover the base or any other salt. Our guide to CEP, DMF and ASMF explains which one you need.
Polymorph and hydrate need to match too. The same salt can exist in more than one crystal form, and those forms can dissolve differently. If your product was developed on one form, the supplier has to make that form, consistently.
What regulators make of a different salt
This is where a well-meant supplier offer can turn into a regulatory project.
In the European Union, different salts of the same active substance are generally treated as the same active substance for a generic application, unless they differ significantly in safety or efficacy. Where a salt does differ significantly, the applicant must provide extra safety or efficacy data, and regulators expect the choice of salt to be justified.
In the United States, a generic filed as an ANDA must contain the same active ingredient as the reference product. A product built on a different salt usually goes through the 505(b)(2) route instead.
Most other regulators follow one of these two approaches, and many ask for bioequivalence data either way. Before you plan any switch, read the guidance from the authority concerned; our directory of drug regulators links to each one.
The practical rule is simple. Buy the same salt, hydrate and crystal form that your registered dossier names. If a supplier offers "the same molecule in a different salt", treat it as a regulatory change, not a purchasing decision.
Related explainers
If you are new to the language of API sourcing, these may help: what an API is and how it is bought, and drug substance versus drug product. Our six-language pharma trade glossary covers the rest of the vocabulary.
How PharmaTradz can help
When you send us an enquiry, tell us the exact form your dossier uses. We match you with manufacturers who make that form and share their document status before you commit to anything. Our documentation and quality pack gathers the CoA, GMP certificate and DMF or CEP references up front, and our supplier verification guide shows how to check them yourself. When you are ready, send us an RFQ.
Frequently Asked Questions(FAQs)
What does hydrochloride mean in a medicine?
It means the active molecule is supplied as a salt made with hydrochloric acid. The salt usually dissolves and keeps better than the pure base, but the medicine's effect comes from the same active molecule either way.
Is hydrochloride harmful?
No. The chloride in a hydrochloride salt is a very small amount of an ion the body already contains in far larger quantities. Whether a medicine is safe depends on the active drug and its dose, not on the hydrochloride part.
Is metformin hydrochloride the same as metformin?
It delivers the same active molecule, but the weights differ: 500 mg of metformin hydrochloride contains about 390 mg of metformin base. The label normally makes clear which of the two the strength refers to.
Can we switch from a hydrochloride API to the base?
Not without a regulatory change. Your dossier names a specific salt, hydrate and crystal form, and a different form needs new data and, in most markets, a variation or a new application.
How should I compare API prices for a salt and a base?
Convert both quotes to cost per kilogram of active moiety. To find how much salt gives the same amount of active, multiply the base amount by the salt's molecular weight divided by the base's molecular weight.
