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API (active pharmaceutical ingredient)

The raw drug substance in a medication that produces its effect — for example, semaglutide itself, before it is formulated into a pen or vial.

By the glp1.how editorial teamReviewed

The active pharmaceutical ingredient (API) is the actual drug molecule in a medication — semaglutide or tirzepatide, as opposed to the water, buffers, and preservatives it's dissolved in. Brand manufacturers make their own API under FDA manufacturing rules; a compounding pharmacy instead buys API in bulk from a supplier and prepares it into a finished product.

Where the API comes from is the single biggest quality question for a compounded GLP-1. Legitimate pharmacies source from FDA-registered facilities and receive a certificate of analysis for each lot, and the FDA has said that semaglutide salt forms (sodium or acetate) are different active ingredients from the base semaglutide in approved drugs, with no lawful basis for compounding. Asking a pharmacy where its API comes from is a fair question; see how compounded GLP-1 medications are made.

The FDA's statement on semaglutide salt forms is in its notice on unapproved GLP-1 drugs (external link).

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Revision history

Updated 1 time since Sep 2, 2026 · show changes
  1. v2

    Body revised

  2. v1

    Change tracking began

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Related terms

  • Compounding pharmacy · A pharmacy licensed to prepare customized medications, including compounded versions of GLP-1 drugs, outside of standard manufacturer production.
  • Tirzepatide · A once-weekly dual GIP and GLP-1 receptor agonist made by Eli Lilly, marketed as Mounjaro for type 2 diabetes and Zepbound for weight management and obstructive sleep apnea.
  • Semaglutide · A GLP-1 receptor agonist medication made by Novo Nordisk, sold under the brand names Ozempic (type 2 diabetes) and Wegovy (weight management), each as an injection or a pill.
  • Certificate of analysis (CoA) · A document reporting the lab test results for a specific batch of a drug ingredient or product, such as identity, purity, and contaminants.
  • GLP-1 · A gut hormone (glucagon-like peptide-1) that stimulates insulin release, slows digestion, and reduces appetite; the target of drugs like semaglutide and liraglutide.
  • Semaglutide salt forms · Versions of semaglutide such as semaglutide sodium and semaglutide acetate, which the FDA says are different active ingredients from the semaglutide base used in approved drugs, with no known lawful basis for compounding.

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