Compounded vs FDA-approved medicines: what’s the difference?
A compounded medicine is made by a licensed pharmacy for one person. Here’s what that means, what the FDA does and doesn’t review, and what to ask your provider.
In short
- An FDA-approved medicine has been reviewed by the FDA for the uses on its label.
- A compounded medicine is prepared by a state-licensed pharmacy for one patient, and the FDA doesn’t review it for safety, effectiveness or quality.
- A provider may prescribe a compounded medicine when no approved product fits, such as a strength or an ingredient that isn’t sold as an approved medicine.
- Being made for you doesn’t make a medicine lower-risk or more effective, so it’s worth asking whether an FDA-approved option would suit you.
Two kinds of prescription medicine
An FDA-approved medicine is made by a drug manufacturer and approved by the FDA for specific uses. A pharmacy dispenses it as the manufacturer makes it, with an FDA-approved label that sets out its uses, directions and warnings. Metformin ER is one example. It’s an FDA-approved generic for type 2 diabetes, and its label carries a boxed warning about lactic acidosis.
A compounded medicine is prepared by a licensed pharmacy for one patient, based on a prescription. The pharmacy prepares it to your provider’s prescription, instead of taking a ready-made box off a shelf. Compounded medicines aren’t FDA-approved. The FDA doesn’t review them for safety, effectiveness or quality before they’re dispensed.
A compounded medicine also isn’t a generic, even when it contains the same active ingredient as a brand-name drug. Generic metformin ER is FDA-approved; a compounded medicine isn’t. So it shouldn’t be called “the same as” a brand, or a “generic” version of one.
Who oversees what
- The FDA approves medicines for specific uses. It doesn’t approve compounded medicines, but federal law and FDA policy set limits on what pharmacies can compound.
- Compounding pharmacies are licensed by the state. Section 503A of federal drug law covers pharmacies that compound for an identified individual patient, on a valid prescription. The pharmacy labels each medicine as state and federal law require.
- Your provider decides whether a treatment is right for you. Providers can also prescribe off-label, meaning for a use the FDA hasn’t specifically approved.
- StackRx is a technology platform, not a pharmacy or a medical practice. It doesn’t compound medicines or make decisions about your care.
Rules on ingredients and copies
Under section 503A, the bulk ingredients a pharmacy uses must meet a USP or NF quality standard (called a monograph) where one exists. They must also be part of an FDA-approved drug or on the FDA’s 503A bulks list. Some other ingredients are compounded under an interim FDA policy while the FDA reviews them. Enclomiphene is one. That policy isn’t an approval, and it can end.
Section 503A also limits compounding that is “essentially a copy” of a medicine already on the market. When a compounded medicine closely matches one that’s sold, the prescriber may need to document a significant difference it makes for that patient.
FDA guidance also cautions telehealth companies against implying that a compounded medicine is the same as, or reviewed like, an approved one. In 2025 and 2026 the FDA sent warning letters to telehealth companies over claims like “same active ingredient as” a brand.
| At a glance | FDA-approved | Compounded |
|---|---|---|
| Who makes it | A drug manufacturer; a pharmacy dispenses it as made | A state-licensed pharmacy, for one patient |
| FDA review | Reviewed for the uses on its label | Not reviewed for safety, effectiveness or quality |
| Label | FDA-approved label with directions and warnings | Labeled by the pharmacy; no FDA-approved label |
| Form and strength | Approved in specific forms and strengths | May combine ingredients, or use them in forms or for purposes that differ from any approved product |
| Example | Metformin ER | Low-dose naltrexone |
Why a provider might prescribe a compounded medicine
Here are a few reasons, with examples from StackRx treatment pages.
- A strength that isn’t sold. Naltrexone is FDA-approved as a 50 mg tablet for alcohol and opioid dependence. There’s no FDA-approved low-dose version, so low-dose naltrexone is compounded. Using it for pain or autoimmune conditions is off-label.
- A brand that’s no longer sold. Vaniqa, a prescription cream for unwanted facial hair, is no longer sold in the US. A pharmacy can compound eflornithine 13.9% instead. It isn’t the same product as Vaniqa, it isn’t FDA-approved, and it hasn’t been tested in trials.
- An ingredient with no approved US product. Estriol, one of the two estrogens in the Bi-Est creams, isn’t in any FDA-approved US product.
- More than one medicine in one application. Some compounded formulas combine ingredients that are FDA-approved on their own. The combination isn’t FDA-approved, and it may never have been tested as a blend.
A compounded medicine isn’t automatically the better choice. For menopause hormones, a 2020 National Academies report found little good evidence on the safety or effectiveness of compounded “bioidentical” hormones. It advised using them only for an allergy to an ingredient in an approved product, or a form that isn’t available. ACOG and The Menopause Society advise against routine compounded hormones when FDA-approved options exist.
Your provider can explain why a compounded medicine may be an option for you and what other options exist, and may recommend an FDA-approved one instead.
What “not FDA-reviewed” means in practice
- The evidence often comes from other products. Studies of an ingredient often tested approved forms or other formulas. Sildenafil was tested in trials of FDA-approved tablets, for example, but the compounded Sildenafil Film hasn’t been tested in any trial. The enclomiphene trials didn’t use compounded capsules.
- There’s no FDA-approved label. The safety information on StackRx pages draws on the labels of approved products with the same ingredients, and on published studies.
- Quality depends on the pharmacy and its ingredients. In 2026 the FDA and CDC reported serious reactions to compounded glutathione injections made with an ingredient not meant for injection.
- The rules can change. An ingredient compounded under the FDA’s interim policy can lose that status if the FDA decides not to add it to the 503A list.
Off-label use is a separate question, and it applies to approved medicines too. Metformin ER is approved only for type 2 diabetes, so using it for prediabetes, insulin resistance or PCOS is off-label. The FDA hasn’t reviewed it for those uses.
Questions to ask your provider
- Is there an FDA-approved option for me? Why might a compounded one fit better?
- Is the way I’d use it off-label?
- What does the research show for this exact formula, and what comes from studies of other forms?
- What side effects should I watch for, and does it interact with anything I take?
- Which pharmacy prepares it, and how can I reach a pharmacist with questions?
- How should I store it, and what’s the beyond-use date on the label?
Safety and when to get help
Any medicine, including a compounded one, can cause side effects or interact with other medicines or conditions. Tell your provider about every medicine and supplement you take, your allergies and health conditions, and whether you’re pregnant, trying to conceive or breastfeeding. A provider decides whether a treatment is right for you and prescribes only if it is.
Each treatment page lists its own safety rules. The main ones for the treatments named above:
- Metformin ER needs a kidney blood test before you start, and it isn’t used when kidney function is very low.
- Low-dose naltrexone can’t be taken with opioid medicines, such as tramadol, codeine, oxycodone or hydrocodone.
- Eflornithine: stop and tell your provider if irritation continues, or if you get a rash, swelling or blisters.
- Bi-Est creams aren’t used in pregnancy. With Bi-Est Vaginal Cream, any vaginal bleeding after menopause needs checking before you start. With Bi-Est Topical Cream, anyone with a uterus also needs a progestogen their clinician prescribes.
- Sildenafil is never taken with nitrate heart medicines, poppers, riociguat or vericiguat.
- Enclomiphene needs bloodwork before you start and along the way. Get help right away for vision changes, pain or swelling in one leg, chest pain or sudden shortness of breath.
- Glutathione injections: get care right away for trouble breathing, swelling, a blistering rash, or fever and chills after a dose.
If you think you’re having a medical emergency, call 911. Get emergency care for chest pain, trouble breathing, or swelling of the face, lips or throat. For severe or worrying side effects, stop the medicine and get medical help, then tell your provider.
Sources
- FDA, Prescription Requirement Under Section 503A (guidance for industry), fda.gov
- FDA, Bulk drug substances used in compounding under section 503A, fda.gov
- FDA, interim 503A bulks policy (January 2025), fda.gov; 503A categories list, May 14, 2026, fda.gov
- FDA, guidance on compounded drugs that are essentially copies of a commercially available drug (503A), fda.gov
- FDA, “What to Know When Promoting Compounded Drugs” (June 15, 2026), fda.gov
- FDA alert on supplement-grade glutathione (August 27, 2026), fda.gov
- NASEM 2020, compounded bioidentical hormone therapy, nationalacademies.org
- ACOG Clinical Consensus 6 (2023), acog.org
- FDA labels: metformin ER (DailyMed); naltrexone 50 mg (Revia and generics); Vaniqa; Viagra (DailyMed, 2026)
- Kim 2016, enclomiphene trials ZA-304/305 (256 men), PubMed 26496621
This article is general information, not medical advice. Only a US-licensed provider who reviews your health can say whether a treatment is right for you. If you have a medical emergency, call 911.
