Drug Substance vs Drug Product

An order that mixes the two terms up asks the wrong supplier for the wrong paperwork. In metformin's case, the powder is the drug substance and the tablet pressed from it is the drug product.

The mix-up is common because the word "bulk" covers both. A drum of metformin powder and a drum of loose metformin tablets are both called bulk, yet they sit on opposite sides of the line. The Good Manufacturing Practice (GMP) rules that apply to them come from different documents.

Dissolution, which measures release of the drug substance from the tablet, is a drug product test, and particle size and crystal form are drug substance checks. A quote that names the wrong side therefore asks for the wrong tests, and the error surfaces late, when the certificate arrives and does not match the item you meant to buy.

A drug substance is the active ingredient, and a drug product is the finished dosage form that contains it. 21 CFR 314.3 defines a drug substance as "an active ingredient that is intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure or any function of the human body, but does not include intermediates used in the synthesis of such ingredient." It defines a drug product as "a finished dosage form, e.g., tablet, capsule, or solution, that contains a drug substance, generally, but not necessarily, in association with one or more other ingredients."

ICH Q7 (the International Council for Harmonisation guideline on API manufacturing) titles its definition "Active Pharmaceutical Ingredient (API) (or Drug Substance)". So the two names are not two manufacturing stages.

An API is a drug substance. An excipient and a finished tablet, capsule or solution belong to the drug product. An intermediate is neither. Tablets or capsules in bulk containers are drug product. The trade term "bulk drug" does not say which side it means, so ask. The table below is read from 21 CFR 314.3, 21 CFR 210.3 and ICH Q7.

Where the drug substance and drug product line falls

21 CFR 210.3 does not define "drug substance". It uses "active ingredient" and defines an inactive ingredient (an excipient) as "any component other than an active ingredient." As of 23 October 2026, the U.S. Food and Drug Administration (FDA) direct final rule published 22 September 2026 (91 FR 60003, Docket FDA-2026-N-5347) adds a definition of "nonclinical study" to 21 CFR 314.3(b), effective 4 February 2027 unless FDA withdraws it after the comment period closes on 7 December 2026. The drug substance and drug product definitions are unchanged.

Drug substance manufacturing follows ICH Q7, while drug product manufacturing follows 21 CFR Part 211. Specification tests also differ: particle size and crystal form are drug substance checks, and dissolution and dosage-unit uniformity are drug product checks.

ICH Q7 covers APIs for human drug products from the point the API starting material (the raw material where Q7 GMP begins) enters the process, and it includes milling and micronizing. 21 CFR Part 211, titled "Current Good Manufacturing Practice for Finished Pharmaceuticals", covers preparation of drug products. Q7 excludes bulk-packaged tablets and capsules, so by reading, those follow the finished-pharmaceutical rules.

Specification tests split the same way, per ICH Q6A, which is written for new chemical drug substances and products. For scale, an FDA training deck gives an example drug substance specification: assay at 98 to 102% by HPLC (high-performance liquid chromatography), related substances (impurities related to the active) at not more than 0.10%, residual solvents at 5000 ppm (parts per million), and water at not more than 2% by Karl Fischer titration (FDA, December 2023). These are illustrative values, not a rule.

A 500 mg metformin hydrochloride tablet is a drug product whose strength is stated on the salt, so it carries about 390 mg of metformin base. A DailyMed label (Cadila Healthcare, dated 2010) opens with the drug substance: metformin hydrochloride, C4H11N5·HCl, molecular weight 165.63. It then describes the drug product: 500 mg film-coated tablets with hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol and povidone. Check the current label for your product, since excipients and coating can change.

The calculation, which can be rerun: the base C4H11N5 weighs 4×12.011 + 11×1.008 + 5×14.007 = 129.17 using standard atomic weights. Then 129.17 ÷ 165.63 = 78.0%, and 500 mg × 0.780 ≈ 390 mg.

The practical consequence is that you should confirm the salt form and assay basis before you convert kilograms of powder into tablets.

Ask for the document that matches the side of the line, and accept it only if it passes the test in the Pass column of the table.

A DMF is never approved or disapproved by FDA. A Type II DMF (the DMF type for drug substances and drug products) covers a drug substance, a drug substance intermediate or a drug product, and the Letter of Authorization lets FDA refer to it for another party's submission (FDA DMF guideline).

Aarise supplies APIs in steroid, peptide, hormone and general pharmaceutical categories, which are drug substances when intended for use in a drug product, and Supplement APIs, which are supplement raw materials rather than drug substances. Peptide APIs come as bulk API powder, not finished vials. On the drug product side, its catalogue covers tablets, capsules, oral liquids, ointments, injections, dry syrup and external applications, and it offers oral-dose contract development and manufacturing from product development through commercial manufacturing. Its AariMet 500 page lists Metformin Hydrochloride IP (Indian Pharmacopoeia) 500 mg per uncoated tablet.

Aarise quotes each API after receiving its name and CAS number, with quantity, destination, grade or purity, documents, payment terms and Incoterms (international shipping terms). Evaluation samples are available to qualified business buyers, with COA, specifications and safety data sheets where applicable. For steroid APIs it does not provide DMF support. Its pharma raw material catalog lists the range, and its guides on choosing between API manufacturer, distributor and CDMO and third-party manufacturing explain how to pick.