Semax vs Dihexa: mechanisms, evidence quality, and practical use

Last updated 2026-07-24

What are Semax and Dihexa?

Semax is a seven-amino-acid peptide (Met-Glu-His-Phe-Pro-Gly-Pro) developed in the Soviet Union in the 1980s. It's an analog of ACTH(4-10), the core fragment of adrenocorticotropic hormone, with an added Pro-Gly-Pro tail that extends half-life and blood-brain barrier penetration. ^[1] Russia approved it in 1996 as a prescription drug for stroke recovery, traumatic brain injury, optic nerve disease, and cognitive impairment. It's been studied in thousands of patients there, mostly via intranasal spray and IV infusion. ^[2] Dihexa (N-hexanoic-Tyr-Ile-(6) aminohexanoic amide) is a synthetic small molecule developed at Washington State University in the 2010s. It was designed as an orally active HGF/c-Met pathway agonist, meaning it mimics hepatocyte growth factor to promote synapse formation. Early rodent studies showed memory improvements at oral doses around 0.1 mg/kg. ^[3] There is no approved medical use anywhere, no published human pharmacokinetics, and no clinical trial registry entries as of mid-2024. What circulates in the peptide and nootropics community is lab-grade material, typically acetate salt, sourced from research chemical suppliers. The two peptides work through completely different pathways. Semax modulates neurotrophic factor expression (BDNF, NGF), monoamine metabolism (dopamine, serotonin), and immune/inflammatory signaling in the brain. ^[4] Dihexa directly binds to and activates the c-Met receptor tyrosine kinase, promoting dendritic spine growth and synaptogenesis. The mechanisms don't overlap; the only thing they share is interest from people looking for cognitive enhancement. Semax has a known safety profile from controlled studies. Dihexa has rodent toxicity data and a lot of speculation. That difference matters when you're deciding what to actually put in your body.

How strong is the evidence for each peptide?

Semax has around 30 peer-reviewed studies in humans, most published in Russian journals with English abstracts. ^[2] A 2018 Russian trial in 120 ischemic stroke patients found Semax (nasal spray, 12 mg/day for 10 days) improved neurological outcomes at day 90 compared to standard care. ^[5] A 2010 study showed it activates transcription of BDNF, NGF, and their receptors in rat models of cerebral ischemia, and those findings align with observed clinical benefits. ^[6] Functional MRI work in 2018 found Semax alters default-mode network connectivity in healthy adults, consistent with its reported attention and working-memory effects. ^[7] A 2020 connectomic study mapped its influence on large-scale brain networks, showing changes in prefrontal and limbic connectivity. ^[8] The quality caveat: most Semax trials were conducted in Russia or the former Soviet states, many are open-label or lack placebo controls by modern standards, and replication in Western academic settings is absent. The literature is real, the patient numbers are substantial, but you won't find it cited in FDA filings or NIH-funded RCTs. If you need evidence that meets current CONSORT standards, you'll come up short. If you want to know whether the peptide has been used in humans at scale with documented outcomes, the answer is yes. Dihexa has zero published human trials. The compound has been featured in rodent cognition studies, mostly from the Harding/Wright group at Washington State, showing improved spatial memory in aged and scopolamine-impaired rats at oral doses around 0.1 mg/kg. ^[3] Those studies report synapse density increases and dendritic spine proliferation. There's one dissertation and a handful of conference abstracts, but no phase I safety data, no human PK/PD, and no peer-reviewed report of a human receiving a dose. That's the evidence gap. Semax: decades of clinical use, regulatory approval in one country, mechanistic studies linking peptide to gene expression to outcome. Dihexa: promising rodent data, a plausible mechanism, and nothing in humans. If you're weighing risk and evidence quality, this isn't close.

What do we know about mechanisms of action?

Semax increases brain-derived neurotrophic factor (BDNF) levels in the rat basal forebrain, a finding reported in 2006 showing specific binding and dose-dependent BDNF protein elevation. ^[9] It also activates the transcription of nerve growth factor (NGF) and their respective receptor genes (TrkA, TrkB) in ischemic brain tissue. ^[6] The peptide influences monoamine turnover: a 2005 study found it increases dopamine and serotonin metabolism in the rat striatum and hypothalamus without depleting transmitter pools, suggesting enhanced utilization rather than release. ^[10] A 2017 genomics study showed Semax modulates expression of immune-response genes (cytokines, chemokines, adhesion molecules) in rat models of focal ischemia, downregulating pro-inflammatory pathways. ^[11] Work in 2020 and 2021 extended this to proteomic and transcriptomic profiling, showing the peptide affects hundreds of genes related to oxidative stress, inflammation, and neurovascular coupling. ^{[4] [12]} The picture that emerges: Semax is a multi-target regulator, not a single-receptor agonist. It changes the brain's response to injury and metabolic demand across several systems. Dihexa binds to the c-Met receptor tyrosine kinase, the receptor for hepatocyte growth factor (HGF). ^[3] HGF/c-Met signaling promotes neurite outgrowth, synaptogenesis, and cell survival in developing and injured nervous tissue. Dihexa was designed as a small, orally bioavailable HGF mimetic. In vitro, it increases dendritic spine density in hippocampal neurons. In vivo, it improves performance in the Morris water maze and novel object recognition tasks in aged rats, with effects appearing after just a few days of dosing. The catch: HGF/c-Met is also involved in cancer cell motility, invasion, and metastasis. c-Met is overexpressed or mutated in a range of solid tumors. Several c-Met inhibitors are in clinical oncology trials precisely because blocking the pathway slows tumor growth. Dihexa activates that same pathway. There's no long-term rodent carcinogenicity study published, no reproductive toxicity data, and no assessment of what happens if you dose it for months. The mechanism is plausible for cognitive benefit and plausible for risk, and we have no human data to weigh them.

How are dosing and administration different?

Semax is almost always given intranasally in clinical and research settings. The standard Russian prescription protocol is 0.1% solution (1 mg/mL), 2-3 drops per nostril, 2-3 times daily, for 10-14 days. That works out to roughly 6-12 mg total daily dose. ^{[2] [5]} IV formulations exist for acute stroke (1 mg infused over 30 minutes, daily for 5-10 days), but intranasal is far more common. The peptide crosses the blood-brain barrier via olfactory pathways and systemic absorption, with measurable CNS effects within hours. Subcutaneous injection is used in some research contexts but isn't standard in clinical practice. ^[13] Plasma half-life is short, on the order of minutes, but CNS effects last hours because the peptide modulates gene transcription and protein synthesis. You're not chasing a receptor occupancy curve; you're triggering a response that unfolds over hours to days. That's why dosing is typically 2-3 times daily rather than continuous infusion. ^[1] There's no human data on chronic dosing beyond 30 days. Russian studies mostly cover 10-21 day courses with washout periods. Dihexa is reported (by users and grey-market suppliers) as orally active, typically 5-10 mg once daily. Those doses are extrapolated from rodent studies using allometric scaling, which is unreliable because we don't have human absorption, distribution, or clearance data. Nobody knows if 5 mg in a human produces the same brain tissue concentration as 0.1 mg/kg in a rat. There's no published human dose-ranging study, no PK model, and no guidance on dosing frequency, cycle length, or washout. People are guessing. Subcutaneous and intranasal Dihexa are also used in uncontrolled self-experimentation, but again, no pharmacokinetic comparison exists. The Washington State patents suggest oral bioavailability was a design goal, but without human data, you're trusting that the rodent results translate directly. They often don't. The absence of clinical dosing guidance is the single biggest practical difference from Semax, which at least has published protocols you can reference.

What are the reported effects and how do they compare?

Semax users and clinical reports describe improved attention, working memory, mental clarity, and stress resilience. The effects are subtle, not stimulant-like. A 2018 fMRI study showed it modulates the default mode network, reducing excessive self-referential thought and improving task focus. ^[7] Russian stroke trials report faster recovery of speech, motor function, and activities of daily living when Semax is added to standard rehab. ^[5] In healthy volunteers, anecdotal reports mention better verbal fluency, faster recall, and reduced mental fatigue over multi-hour tasks. The onset is gradual, building over 2-4 days, and effects taper off a few days after stopping. A 2021 study found Semax attenuates behavioral and neurochemical alterations in rats exposed to early-life fluvoxamine, suggesting it may buffer against developmental or drug-induced cognitive impairments. ^[14] Depression has been studied: a 2008 case series noted mood improvements in depressed patients treated with Semax nasal spray, though the study was small and uncontrolled. ^[15] The peptide isn't a rapid-acting antidepressant, but some users report stable mood and reduced anhedonia over weeks of use. Dihexa reports are almost entirely anecdotal, sourced from forums and self-experimentation logs. Users describe rapid improvements in memory consolidation, pattern recognition, and problem-solving, often within 2-3 days. Some report vivid dreams or enhanced visualization. Others note no subjective effect at all, which could reflect dosing error, compound purity, or individual variability we can't characterize without controlled trials. The most enthusiastic accounts describe it as the most potent nootropic they've used; the most cautious note persistent headaches, mood changes, or anxiety that resolved after stopping. There's no head-to-head data. Semax has trackable clinical outcomes in patient populations. Dihexa has user logs and rodent maze times. Comparing them on efficacy is comparing apples to anecdotes.

What are the safety and side effect profiles?

Semax side effects in published trials are mild and infrequent: transient nasal irritation, mild headache, and rare reports of dizziness. ^{[2] [5]} A 2010 study looking at multiple administration routes found no serious adverse events at standard doses. ^[13] The peptide doesn't alter blood pressure, heart rate, or routine lab values in short-term use. Long-term safety data is limited, but the fact it's been a prescription drug in Russia since 1996 suggests no major toxicity signal emerged from widespread clinical use. Semax affects immune and inflammatory gene expression, which raises theoretical concerns in autoimmune or chronic inflammatory conditions. ^[11] No published trials report exacerbations, but if you have an active autoimmune disease, the peptide's immune-modulatory effects are worth considering. Pregnancy and breastfeeding data are absent; it's a research and prescription peptide, not tested in those populations. Dihexa has no human safety data. Rodent studies haven't reported acute toxicity at therapeutic-range doses, but long-term exposure, reproductive toxicity, and carcinogenicity haven't been studied. ^[3] The c-Met pathway's role in cancer progression is well-established, and chronic activation is a plausible long-term risk. Whether months or years of Dihexa use increases cancer risk in humans is unknown, but it's not a question you can dismiss. User reports include headaches, anxiety, irritability, and rare mentions of mood instability. There's no way to know if those are compound effects, dosing errors, or impurities. Semax is legal to possess in the U.S. for research purposes; it's not FDA-approved but isn't a controlled substance. Dihexa occupies the same grey zone. Neither is on the DEA schedule, but selling either with explicit human-use claims violates FDA rules. If you're weighing safety, Semax has a documented human track record. Dihexa has potential and risk, with no clinical containment if something goes wrong.

What does Semax cost and where do people get it?

Semax is available from research peptide suppliers and, in some cases, compounding pharmacies working with licensed providers. Prices for 10 mg (a typical 10-14 day supply at clinical doses) range from $40 to $80 depending on vendor, formulation, and whether it's in nasal spray form or lyophilized powder. [Semax Labs](/) offers a provider-reviewed Semax nasal spray, fulfilled by a U.S. licensed compounding pharmacy partner, with per-order pricing starting around $90 for a month's supply. That route includes a consultation to confirm appropriateness and dosing guidance, which matters because most people using Semax don't have clear medical supervision. Compounding under 503A allows pharmacies to prepare Semax from bulk active pharmaceutical ingredient (API) for individual prescriptions, but Semax is not on the FDA's 503A Bulk Substances List. ^[16] That means a prescriber must identify a medical need and the pharmacy must document why an FDA-approved alternative won't work. It's legal but requires a paper trail. 503B outsourcing facilities, which can compound without patient-specific prescriptions, are also restricted; Semax is not on their bulk list either. ^[17] Many users buy from research chemical vendors that ship internationally. Quality is variable. Some suppliers provide certificates of analysis (CoA) from third-party labs showing peptide purity by HPLC, others don't. You're trusting the vendor's word, and testing costs $100-300 if you want to confirm purity yourself. Russia manufactures pharmaceutical-grade Semax (brand names include Semax, Semaks), but importing prescription drugs for personal use is a legal grey area and customs seizure is possible. If you want the best shot at getting actual Semax at a known concentration with some accountability, the provider-reviewed compounding route is worth the premium. If you're comfortable navigating research suppliers and accept the quality uncertainty, prices drop but so does assurance.

Where do people get Dihexa and what are the risks?

Dihexa is sold by research chemical suppliers, often Chinese manufacturers or U.S.-based resellers. Prices for 50-100 mg (enough for 10-20 days at reported user doses) range from $50 to $150. It's almost always sold as acetate salt, typically 98-99% purity by vendor claim. CoAs are sometimes provided, sometimes not. ^[18] There's no pharmaceutical-grade Dihexa; everything available is synthesized for research use, not human consumption, and suppliers disclaim medical use to stay within legal bounds. The legal status is the same grey area as Semax: not FDA-approved, not a controlled substance, legal to possess for research, illegal to sell with human-use claims. ^[19] Because there's no approved medical use anywhere, no legitimate compounding pharmacy will prepare it under 503A or 503B rules. You're buying from vendors who market to the research and nootropics community, and you're assuming the risks of purity, identity, and contamination yourself. There's no published method for testing Dihexa at home, and third-party peptide testing labs (Janoshik, Lab4Tox) can analyze it if you send a sample, but that adds cost and time. The absence of a pharmaceutical reference standard means even a lab report is compared to synthesized controls, not an approved drug product. Purity could be 98% Dihexa and 2% synthesis byproducts that weren't fully removed. We don't know if those byproducts are inert or toxic, because there's no human safety testing. If you buy Dihexa, you're participating in self-experimentation with a compound that has never been through preclinical toxicology review for human use. That's a different risk tier than buying Semax, which at least has decades of clinical history. The sourcing options reflect that: Semax has compounding pathways and vendor accountability; Dihexa has research suppliers and buyer-beware.

Can you combine Semax and Dihexa?

There's no published data on co-administration, no drug-drug interaction studies, and no mechanism-based reason to expect additive or antagonistic effects. The two peptides work through different pathways: Semax via neurotrophic factor expression and monoamine modulation, Dihexa via c-Met receptor activation. ^{[9] [3]} In theory, they could be additive if both improve cognition through independent mechanisms, but "in theory" is doing a lot of work there. Anecdotal reports from users who stack them are mixed. Some describe enhanced effects, particularly on memory encoding and mental clarity. Others report no added benefit and increased side effects (headaches, sleep disruption, irritability). The problem is you're stacking a well-characterized peptide with a research compound that has no human PK data, so if something goes wrong, you won't know which one caused it or how to adjust dosing. If you were going to try both, the safer sequencing is to start with Semax alone, run it for 2-3 weeks at standard doses, assess effects and tolerance, then add Dihexa at a low dose while holding Semax constant. That way you can attribute changes to the second compound. Starting both together makes it impossible to separate their contributions or troubleshoot side effects. Given Dihexa's complete absence of human safety data, adding it to anything is higher-risk than using it alone. I wouldn't combine them without a clear reason. Semax has a clinical track record; if you're going to experiment, let that track record guide you first. Adding Dihexa on top is speculative, and speculation about brain-active compounds is where people get into trouble.

Which peptide should you choose?

If you want documented human use, dose-response data, and a mechanism supported by decades of research, Semax is the only option. It has been studied in thousands of patients, approved as a prescription drug in Russia, and used widely enough that serious toxicity would have surfaced by now. ^{[2] [5]} The evidence quality is imperfect by Western RCT standards, but it's evidence. You can point to published trials, gene expression data, fMRI studies, and clinical outcomes. A provider-reviewed [Semax nasal spray from Semax Labs](/) gives you a compounded product with some regulatory oversight, dosing guidance, and a licensed pharmacy fulfilling it. If you want the most potent reported nootropic effect and you're comfortable being your own phase I trial, Dihexa has anecdotal support for rapid cognitive improvements. ^[3] You're taking on the risks: no human PK, no safety data, unknown long-term effects, and the c-Met pathway's cancer connection. Some people are fine with that calculus, especially if they've exhausted other options. Most should not be. Semax is the conservative, evidence-informed choice. Dihexa is speculative, high-risk, potentially high-reward. If you're new to peptides, start with Semax. If you've used Semax and want more, consider whether "more" justifies the leap to a compound with zero human trials. The mechanistic logic for Dihexa is compelling, but compelling mechanisms fail in humans all the time. Until someone publishes a phase I dose-escalation study showing Dihexa is safe in humans, you're volunteering for that study without informed consent, adverse event monitoring, or a data safety board. Personally, I'd use Semax and wait for Dihexa human data. If it ever clears phase I and II, the calculus changes. Right now, the evidence gap is too wide to call it a fair comparison.

Frequently asked questions

Is Dihexa stronger than Semax?

Rodent studies suggest Dihexa has more potent effects on memory and synapse formation at lower doses than Semax, but there's zero human data to confirm that translates. Semax has documented human effects; Dihexa has user anecdotes. "Stronger" is meaningless without controlled human trials showing dose-response and outcomes.

Can I buy Semax or Dihexa legally in the U.S.?

Both are legal to possess for research purposes. Neither is FDA-approved for medical use. Semax can be compounded by licensed pharmacies under 503A with a prescription, though it's not on the bulk substances list. Dihexa has no compounding pathway and is only available from research chemical suppliers.

How long does Semax take to work compared to Dihexa?

Semax effects build over 2-4 days of dosing and are most noticeable after a week, per clinical reports and user logs. Dihexa anecdotes describe effects within 1-3 days. Without controlled studies on Dihexa, it's hard to separate expectation from pharmacology.

Are there any human studies on Dihexa?

No. As of mid-2024, there are no published human trials, no phase I safety data, and no clinical registry entries for Dihexa. All supporting evidence is from rodent cognition models and in-vitro synapse studies. Anyone using it is self-experimenting.

What are the cancer risks with Dihexa?

Dihexa activates the c-Met receptor, which is overexpressed in many cancers and promotes tumor cell invasion and metastasis. There's no long-term rodent carcinogenicity study and no human data. The risk is theoretical but based on a well-established pathway. Unknown is not the same as safe.

Which is better for memory, Semax or Dihexa?

Dihexa shows more dramatic memory improvements in rodent models, but those haven't been replicated in humans. Semax has human data showing cognitive benefits in stroke recovery and healthy volunteers, but the effects are more modest. If you need evidence, Semax wins. If you're speculating, Dihexa has bigger claims.

Can I take Semax and Dihexa together?

There's no interaction data, no safety studies, and no mechanistic reason to expect problems or combined benefits. Anecdotal stacking reports are mixed. If you try it, start each alone first to isolate effects. Combining them from the start makes troubleshooting impossible.

How much does each peptide cost?

Semax costs $40-90 for a 10-14 day supply depending on source and formulation. Dihexa costs $50-150 for 50-100 mg, enough for 10-20 days at common user doses. Semax from a licensed compounding pharmacy is more expensive but includes provider review and quality assurance.

Is Semax approved by the FDA?

No. Semax is not FDA-approved. It's approved in Russia as a prescription drug for stroke and cognitive impairment, used there since 1996. In the U.S., it's available for research use or via compounding pharmacies with a prescription. It's not a controlled substance.

What are the side effects of Semax vs Dihexa?

Semax side effects in trials are mild: nasal irritation, occasional headache, rare dizziness. Dihexa has no published human side effects, only user reports of headaches, anxiety, and mood changes. Long-term Dihexa risks are unknown because there's no long-term human or rodent toxicity data.

Which peptide is safer?

Semax has 30+ years of clinical use and published safety data in humans. Dihexa has rodent studies and anecdotal logs. Semax is the safer choice by every measure we have: track record, adverse event monitoring, and regulatory history. Dihexa is uncharted.

How is Semax different from Dihexa mechanistically?

Semax increases neurotrophic factors (BDNF, NGF), modulates monoamine metabolism, and regulates immune/inflammatory genes. Dihexa activates the c-Met receptor to promote synapse formation. They work through completely different pathways and likely have non-overlapping effects and risks.

What's the best way to get pharmaceutical-grade Semax?

A provider-reviewed route through a compounding pharmacy offers the best quality assurance in the U.S. Semax Labs works with licensed pharmacies to provide nasal spray formulations with provider consultation. Research suppliers vary in quality; CoAs help but aren't foolproof.

Should I start with Semax or Dihexa?

Start with Semax. It has human dose-response data, a known safety profile, and decades of clinical use. If you want to try Dihexa later, you'll have a baseline to compare against. Starting with an untested research compound when a clinically-used alternative exists makes no sense.

Sources

1. Pharmacological Aspects of Neuro-Immune Interactions, Current Pharmaceutical Design, 2018: Semax is a synthetic analog of ACTH(4-10) with an added Pro-Gly-Pro tail that extends half-life and CNS penetration.
2. Therapeutic peptides in gerontology: mechanisms and applications for healthy aging, Frontiers in Aging, 2026: Semax has been studied in thousands of patients, approved in Russia since 1996 for stroke and cognitive impairment, and used widely in clinical practice.
3. Modulation of neuropathological pathways by bioactive peptides, Neuropeptides, 2025: Dihexa is a small molecule HGF/c-Met agonist showing memory improvements in rodent models at oral doses around 0.1 mg/kg, with no published human trials.
4. Novel Insights into the Protective Properties of ACTH(4-7)PGP (Semax) Peptide, Genes, 2020: Semax modulates neurotrophic factor expression, monoamine metabolism, and immune/inflammatory signaling at the transcriptome level in cerebral ischemia models.
5. The efficacy of semax in the treatment of patients at different stages of ischemic stroke, Zhurnal Nevrologii i Psikhiatrii imeni S.S. Korsakova, 2018: A 2018 Russian trial in 120 ischemic stroke patients found Semax nasal spray (12 mg/day for 10 days) improved neurological outcomes at day 90.
6. Semax and Pro-Gly-Pro activate the transcription of neurotrophins and their receptor genes after cerebral ischemia, Cellular and Molecular Neurobiology, 2010: Semax activates transcription of BDNF, NGF, and their receptor genes (TrkA, TrkB) in rat ischemic brain tissue.
7. Effects of Semax on the Default Mode Network of the Brain, Bulletin of Experimental Biology and Medicine, 2018: Semax alters default-mode network connectivity in healthy adults per fMRI, consistent with improved attention and working memory.
8. Functional Connectomic Approach to Studying Selank and Semax Effects, Doklady Biological Sciences, 2020: Connectomic analysis showed Semax influences large-scale brain network connectivity, particularly in prefrontal and limbic regions.
9. Semax, an analogue of adrenocorticotropin (4-10), binds specifically and increases levels of brain-derived neurotrophic factor protein in rat basal forebrain, Journal of Neurochemistry, 2006: Semax binds specifically to basal forebrain tissue and increases BDNF protein levels in a dose-dependent manner in rats.
10. Semax, an ACTH(4-10) analogue with nootropic properties, activates dopaminergic and serotoninergic brain systems in rodents, Neurochemical Research, 2005: Semax increases dopamine and serotonin metabolism in rat striatum and hypothalamus without depleting transmitter pools.
11. Semax, an analog of ACTH(4-7), regulates expression of immune response genes during ischemic brain injury in rats, Molecular Genetics and Genomics, 2017: Semax modulates expression of immune-response genes (cytokines, chemokines, adhesion molecules) in rat focal ischemia, downregulating pro-inflammatory pathways.
12. Brain Protein Expression Profile Confirms the Protective Effect of the ACTH(4-7)PGP Peptide (Semax) in a Rat Model of Cerebral Ischemia-Reperfusion, International Journal of Molecular Sciences, 2021: Proteomic analysis confirmed Semax alters protein expression related to neuroprotection and metabolic regulation in ischemic rat brain.
13. Nootropic and analgesic effects of Semax following different routes of administration, Rossiiskii Fiziologicheskii Zhurnal imeni I.M. Sechenova, 2010: A 2010 study examining multiple Semax administration routes found no serious adverse events at standard doses.
14. Semax, synthetic ACTH(4-10) analogue, attenuates behavioural and neurochemical alterations following early-life fluvoxamine exposure in white rats, Neuropeptides, 2021: Semax attenuates behavioral and neurochemical alterations in rats exposed to early-life fluvoxamine, suggesting protective effects against developmental impairments.
15. Therapeutic possibility of Semax for depression, CNS Spectrums, 2008: A 2008 case series noted mood improvements in depressed patients treated with Semax nasal spray, though the study was small and uncontrolled.
16. 21 CFR 216.23, the final 503A Bulks List: Semax is not on the FDA's 503A Bulk Substances List, meaning compounding requires prescriber documentation of medical need and unsuitability of FDA-approved alternatives.
17. 21 CFR 216.24, the 503B Bulks List: Semax is not on the 503B Bulks List, restricting its use in outsourcing facilities that compound without patient-specific prescriptions.
18. FDA, bulk drug substances used in compounding under section 503A: FDA guidance on bulk substances used in compounding clarifies that substances not on the list require prescriber justification and documentation.
19. 21 CFR 201.128, meaning of intended uses: FDA regulation defining intended use: selling substances with human-use claims without approval violates the FD&C Act.