Compound Monograph
Huperzine-B
Huperzine B is a lycodine-type Lycopodium alkaloid from firmoss (Huperzia serrata) and a reversible, AChE-selective cholinesterase inhibitor — weaker than huperzine A but more selective — studied preclinically for cognition and neuroprotection. No human isolate trials; the human anti-Alzheimer evidence belongs to huperzine A.
Sources · 3
Where Does It Come From?
Huperzine-B is a naturally occurring lycopodium alkaloid, found in Firmoss and 2 other sources. It is well tolerated orally (low toxicity).
Concentration
Content by Source
Concentrations not reported. No percent-dry-weight or mg/g figures have been published for this compound in its source plants.
Huperzine-B at a Glance
Huperzine B is a lycodine-type Lycopodium alkaloid from firmoss, and the less-studied sibling of huperzine A.
It is a reversible cholinesterase inhibitor with a different balance of properties: weaker than huperzine A but more selective for acetylcholinesterase, which in principle means fewer of the peripheral effects that come from inhibiting butyrylcholinesterase too.
Its research is preclinical, covering cognition and neuroprotection.
What It's Used For
Huperzine B is a lycodine-type Lycopodium alkaloid from firmoss (Huperzia serrata) 10Reference 10ReviewHuperzine A from Huperzia species — an ethnopharmacological reviewView study → and the weaker, more selective sibling of the famous huperzine A. The honesty gate for the whole page: the human anti-Alzheimer/nootropic evidence — RCTs, meta-analyses and the negative independent US Phase II trial — belongs to huperzine A, not B. Huperzine B’s own literature is preclinical (Chinese pharmacology from 1987–2002 plus a few structural/in-vitro papers): it is a genuine reversible, AChE-selective cholinesterase inhibitor, roughly twice as weak as huperzine A but markedly more selective for AChE over butyrylcholinesterase.
Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. No human isolate data, so scores stay low by design.
Huperzine B is a genuine reversible acetylcholinesterase inhibitor: it binds Torpedo AChE with a dissociation constant of ~0.33 µM (vs ~0.18 µM for huperzine A) at the same anionic subsite, triggering the same oxyanion-hole peptide flip 1Reference 1X-ray structures of Torpedo californica acetylcholinesterase complexed with (+)-huperzine A and (−)-huperzine B: structural evidence for an active-site rearrangementView study →; in mice it is highly AChE-over-BuChE selective (BuChE:AChE IC50 ratio ~66, vs 0.54 for tacrine) and less toxic than tacrine 2,
Gap: no human isolate trials for Alzheimer’s — all positive human dementia data are huperzine A — and the “wider therapeutic margin” is inferred from selectivity plus a tacrine (not huperzine A) toxicity comparison, not a therapeutic-index study 2Reference 2AnimalInhibitory effects of huperzine B on cholinesterase activity in miceView study →.
Two early Chinese behavioral studies found huperzine B improved impaired memory and facilitated learning/spatial-discrimination memory in mice 6,
Gap: small, dated (1987–88), with no dose-response replication and no human data — direction-of-effect only, and huperzine B was consistently the weaker of the two alkaloids 6,
Huperzine B attenuated H₂O₂-induced injury in PC12 cells (preserving glutathione peroxidase/catalase, lowering malondialdehyde) 4Reference 4Huperzine B, a novel acetylcholinesterase inhibitor, attenuates hydrogen-peroxide-induced injury in PC12 cellsView study → and protected them against oxygen-glucose-deprivation injury 5Reference 5AnimalHuperzine B protects rat pheochromocytoma cells against oxygen-glucose-deprivation-induced injuryView study →; a bis-huperzine-B derivative reproduced this against amyloid-β and apoptotic stress (supportive context only) 9Reference 9Pharmacodynamic study of FS-0311, a novel highly potent, selective acetylcholinesterase inhibitor (a bis-huperzine-B derivative)View study →.
Gap: in-vitro only, at micromolar concentrations far above plausible CNS exposure, and shared by all cholinesterase inhibitors tested — not huperzine-B-specific 4,
Mechanisms
| Target / pathway | Effect | Relevant to |
|---|---|---|
| Acetylcholinesterase (AChE) | reversible inhibition (Kd ~0.33 µM); anionic-subsite binding, oxyanion-hole flip | cognitionanti-AD |
| AChE-vs-BuChE selectivity | strongly AChE-selective (more so than tacrine) | safety margin / fewer peripheral effects |
| Oxidative-stress defense | ↑ GSH-peroxidase, catalase, SOD; ↓ malondialdehyde (stressed PC12) | neuroprotection (in-vitro) |
| NMDA / glutamate; NGF / Nrf2 / APP | not established for huperzine B (documented for huperzine A only) | — (not attributed to B) |
Pharmacokinetics
Huperzine B is a small, basic lycodine-type alkaloid, and its human pharmacokinetics are unknown — no isolate PK studies exist. In mice, a single oral dose produced steady-state brain AChE inhibition within ~4 h, indicating oral absorption and blood-brain-barrier penetration in rodents 2Reference 2AnimalInhibitory effects of huperzine B on cholinesterase activity in miceView study →; its half-life is not characterized for huperzine B (huperzine A’s ~5–14 h in humans should not be transferred to it). It is present at low levels in Huperzia serrata alongside huperzine A and is typically co-isolated by chromatography.
Clinical trials
There are no robust human clinical trials of isolated huperzine B for any indication. The dementia/cognition RCTs, meta-analyses and the negative US Phase II trial all concern huperzine A (see huperzine A) — no human efficacy should be presented for huperzine B.
| Completed | Planned | Terminated | Preclinical |
|---|---|---|---|
| —(none, isolate) | — | — | Modest(older Chinese pharmacology + in-vitro) |
Last checked: July 2026.
Toxicity & Safety
Huperzine B rates below huperzine A on lower potency and better enzyme selectivity, but the framing that matters is this: it is a cholinesterase inhibitor, not a benign nutrient, and there is essentially no human exposure data behind the rating.
- Weaker and more selective than huperzine A. Roughly 2x lower binding affinity, markedly more AChE-over-BuChE selective, and less toxic than tacrine in mice.
- Not a benign nutrient. As a cholinesterase inhibitor it carries the class cholinergic ceiling — nausea, GI upset, sweating, bradycardia — at sufficient dose.
- Avoid in pregnancy and lactation. No reproductive data for a brain-penetrant cholinesterase inhibitor.
- Do not combine with other cholinergic drugs. Including other cholinesterase inhibitors.
- No human isolate exposure data. The low rating reflects lower potency and selectivity, not a demonstrated human safety record.
Full Safety & Interactions Detail
Huperzine B carries a provisional low flag — it is a genuinely active but weaker AChE inhibitor than huperzine A (~2× lower binding affinity), with markedly higher AChE-over-BuChE selectivity and lower toxicity than tacrine in mice 1,
Dosage
There is no established human dose for isolated huperzine B — it is not sold as a standalone standardized supplement, occurring only as a minor co-alkaloid in Huperzia serrata extracts standardized to huperzine A. (The nootropic figure of ~50–200 µg/day belongs to the huperzine A page, not here.)
References
- Dvir H, et al. (2002). X-ray structures of Torpedo californica acetylcholinesterase complexed with (+)-huperzine A and (−)-huperzine B: structural evidence for an active-site rearrangement. Biochemistry. https://pubmed.ncbi.nlm.nih.gov/12196020/
- Liu J, et al. (1999). Inhibitory effects of huperzine B on cholinesterase activity in mice. Acta Pharmacologica Sinica. https://pubmed.ncbi.nlm.nih.gov/10437161/
- Xu H, Tang XC (1987). Cholinesterase inhibition by huperzine B. Acta Pharmacologica Sinica. https://pubmed.ncbi.nlm.nih.gov/2955654/
- Zhang HY, Tang XC (2000). Huperzine B, a novel acetylcholinesterase inhibitor, attenuates hydrogen-peroxide-induced injury in PC12 cells. Neuroscience Letters. https://pubmed.ncbi.nlm.nih.gov/10996445/
- Wang ZF, et al. (2002). Huperzine B protects rat pheochromocytoma cells against oxygen-glucose-deprivation-induced injury. Acta Pharmacologica Sinica. https://pubmed.ncbi.nlm.nih.gov/12466060/
- Zhu XD, Tang XC (1988). Improvement of impaired memory in mice by huperzine A and huperzine B. Acta Pharmacologica Sinica. https://pubmed.ncbi.nlm.nih.gov/3256210/
- Zhu XD, Tang XC (1987). Facilitatory effects of huperzine A and B on learning and memory of spatial discrimination in mice. Acta Pharmaceutica Sinica. https://pubmed.ncbi.nlm.nih.gov/3452959/
- Yan XF, et al. (1987). Effects of huperzine A and B on skeletal muscle and the electroencephalogram. Acta Pharmacologica Sinica. https://pubmed.ncbi.nlm.nih.gov/2958995/
- Wang ZF, et al. (2008). Pharmacodynamic study of FS-0311, a novel highly potent, selective acetylcholinesterase inhibitor (a bis-huperzine-B derivative). Cellular and Molecular Neurobiology. https://pubmed.ncbi.nlm.nih.gov/17786550/
- Ma X, et al. (2007). Huperzine A from Huperzia species — an ethnopharmacological review. Journal of Ethnopharmacology. https://pubmed.ncbi.nlm.nih.gov/17644292/
