Ziconotide
A cone snail toxin turned into a spinal painkiller for pain nothing else has touched, with psychiatric risks to match
Ziconotide is a synthetic copy of a peptide from the venom of a fish-hunting cone snail. It blocks N-type calcium channels in the spinal cord's pain pathways. Approved in 2004 as Prialt, it is infused into the spinal fluid for severe chronic pain that other treatments, intrathecal morphine included, have not controlled.
What is it?
Ziconotide is not an opioid; its label calls it a non-opioid, non-NSAID analgesic. It blocks the N-type calcium channels that pain-signalling nerves use to pass their message on in the spinal cord. The peptide began as one of the cone snail toxins described in the 1980s, and it works only when delivered to the spinal fluid, through an implanted or external microinfusion pump; the label says it is not for intravenous use.
Its target is now visible in detail: cryo-electron microscopy of the human channel shows the peptide plugging the outer mouth of the pore. In the spinal fluid it has a half-life of about 4.6 hours, and during continuous infusion plasma levels were too low to measure in more than half of patients.
The label starts at no more than 2.4 mcg a day, rising by up to 2.4 mcg no more than two or three times a week to a recommended maximum of 19.2 mcg a day by day 21. Its boxed warning is about the mind: severe psychiatric symptoms and neurological impairment can occur, it is contraindicated in anyone with a history of psychosis, and it should be stopped if serious signs appear.
The trials trace a trade between speed and tolerability. Titrated over five or six days in cancer and AIDS pain, it improved pain scores by 53% against 18% on placebo. Titrated slowly over three weeks to a much lower dose, it improved them by 14.7% against 7.2%, but was far better tolerated. Pooled, the trials show real pain relief and adverse events in almost everyone treated.
Practice has moved toward lower doses and combinations. A registry of 93 patients found that about one in six had meaningful relief at 12 weeks and nearly four in ten of those still treated at 18 months. In 211 cancer patients, ziconotide at a median 1.6 µg a day alongside morphine and local anaesthetics came with an 89.7% median cut in oral opioids, though drowsiness, confusion and hallucinations were common early on. Its place is narrow by design: for people whose pain has defeated the alternatives.
Mechanism of Action
Ziconotide is the synthetic form of a 25-amino-acid cone snail toxin that blocks N-type (Cav2.2) calcium channels on pain-carrying nerves in the spinal cord.
N-type calcium channels
Binds Cav2.2 channels on A-delta and C fibres in the superficial dorsal horn (label).
Signal blocked at the synapse
In animals, blocking these channels stops the release of excitatory transmitters from pain-fibre terminals (label).
Spinal fluid only
Given intrathecally by pump; it is cleared from spinal fluid with a half-life of about 4.6 hours and is not for intravenous use (label).
Published Research
These are the studies in people, read from their PubMed abstracts, with dosing from the Prialt label read October 1, 2026.
Fast titration, cancer and AIDS pain
In a randomised, double-blind trial in 111 people with refractory cancer or AIDS pain, nearly all already on opioids, ziconotide titrated over five to six days improved pain scores by 53.1%, against 18.1% on placebo. Half the patients responded, against 17.5%, and five had complete relief.
Slow titration, chronic pain
In 220 adults with severe chronic pain, a slow three-week titration to a mean of 6.96 mcg a day improved pain by 14.7%, against 7.2% on placebo (p = 0.036). Dizziness, confusion, unsteadiness and memory impairment were the notable adverse events, and it was better tolerated than the two earlier, faster trials.
Long-term open-label use
Of 644 patients, 119 stayed on treatment for a year or more. Median pain scores moved from 76 at baseline to 68 at one month and 73 at the last observation up to month two. Almost all (99.7%) had at least one adverse event, most mild or moderate.
PRIZM registry: final results
Of 93 patients in a registry, 17.4% had at least 30% less pain at 12 weeks and 38.5% of the 28 still treated at 18 months; nearly all had adverse events, most often nausea (25.8%), confusion (22.6%) and dizziness (20.4%).
Cancer pain in routine practice
In 211 cancer patients given low-dose ziconotide with morphine and local anaesthetics (median 1.6 µg a day at three months), pain fell in most and median oral opioid use dropped 89.7%; drowsiness (51%), confusion (46%) and hallucinations (40%) were common, mostly early and mostly resolving.
First-line for neuropathic pain
In 14 patients started on intrathecal ziconotide as their first intrathecal drug, 7 of 11 followed for about 11 months responded, with gains in pain, disability and emotional well-being.
The psychiatric signal
A case report and scoping review collected 21 published cases, from 9 case reports and 4 case series, of people on ziconotide who developed symptoms ranging from psychosis to delirium.
Meta-analysis: benefit and harm
Pooled trials showed a mean pain reduction of 22.5 points against placebo, with adverse events in 94.9% against 76.9% and serious adverse events in 17.9%; effects on opioid use were inconsistent across randomised trials.
The three randomised trials
A systematic review of the three placebo-controlled trials found a pooled odds ratio of 2.77 for responding on ziconotide, and noted that frequent serious adverse events led two of them to revise their protocols.
Structure of the blocked channel
Cryo-electron microscopy of human Cav2.2 showed ziconotide sitting in the channel's outer pore, held by the helices around the selectivity filter and the extracellular loops of three repeats.
Dosing Data
Prialt is infused into the spinal fluid by pump, starting at no more than 2.4 µg a day and rising slowly to at most 19.2 µg a day.
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Side Effects & Contraindications
Reported Side Effects
From the Prialt label (SPL version 4, effective September 15, 2026) and the studies.
Contraindications & Cautions
From the label.
Legal Status
Approved for severe chronic pain, by intrathecal infusion only.
Frequently Asked Questions
?Is ziconotide an opioid?
No. It blocks N-type calcium channels; the label calls it a non-opioid, non-NSAID analgesic.
?How is it given?
Only into the spinal fluid, by an implanted or external pump, starting at 2.4 mcg a day and rising slowly to at most 19.2 mcg a day.
?Why does it carry a boxed warning?
Because severe psychiatric symptoms and neurological impairment can occur. It is contraindicated after any history of psychosis, and patients are monitored for confusion, hallucinations and mood changes.
?Can ziconotide be combined with morphine?
In practice it often is. In 211 cancer patients it was given at low doses together with intrathecal morphine and local anaesthetics, and median oral opioid use fell by 89.7%. The label itself warns that opioids must not be stopped abruptly when starting it; they are tapered over a few weeks.
References
- [fda-pi] Prialt (ziconotide) intrathecal infusion prescribing information, boxed warning and sections 1, 2, 4, 5, 6 and 12.3 (DailyMed SPL version 4, effective September 15, 2026; read October 1, 2026).
- [pubmed] Staats PS, et al. "Intrathecal ziconotide in the treatment of refractory pain in patients with cancer or AIDS: a randomized controlled trial." JAMA, 2004;291(1):63-70. PMID: 14709577.
- [pubmed] Rauck RL, et al. "A randomized, double-blind, placebo-controlled study of intrathecal ziconotide in adults with severe chronic pain." J Pain Symptom Manage, 2006;31(5):393-406. PMID: 16716870.
- [pubmed] Wallace MS, et al. "Intrathecal ziconotide for severe chronic pain: safety and tolerability results of an open-label, long-term trial." Anesth Analg, 2008;106(2):628-37, table of contents. PMID: 18227325.
- [pubmed] Peraire M, et al. "Ziconotide and psychosis: from a case report to a scoping review." Front Mol Neurosci, 2024;17:1412855. PMID: 39479264.
- [pubmed] Olivera BM, et al. "Peptide neurotoxins from fish-hunting cone snails." Science, 1985;230(4732):1338-43. PMID: 4071055.
- [pubmed] McDowell GC, et al. "Effectiveness and Safety of Intrathecal Ziconotide: Final Results of the Patient Registry of Intrathecal Ziconotide Management (PRIZM)." Pain Med, 2020;21(11):2925-2938. PMID: 32472137.
- [pubmed] Dupoiron D, et al. "Real-Life Data on Ziconotide-Based Intrathecal Therapy in Patients With Cancer Pain: Interim Analysis of the Observational Practice in Clinics Registry." Neuromodulation, 2026. PMID: 42189020.
- [pubmed] Shao MM, et al. "Effect of First-Line Ziconotide Intrathecal Drug Therapy for Neuropathic Pain on Disability, Emotional Well-Being, and Pain Catastrophizing." World Neurosurg, 2021;145:e340-e347. PMID: 33096281.
- [pubmed] Picañol J, et al. "Efficacy and safety of the Ca(v)2.2 blocker Ziconotide in pain: a meta-analysis and systematic review." Pain Rep, 2025;10(6):e1363. PMID: 41255849.
- [pubmed] Brookes ME, et al. "Ziconotide Monotherapy: A Systematic Review of Randomised Controlled Trials." Curr Neuropharmacol, 2017;15(2):217-231. PMID: 26861472.
- [pubmed] Gao S, et al. "Structure of human Ca(v)2.2 channel blocked by the painkiller ziconotide." Nature, 2021;596(7870):143-147. PMID: 34234349.
Sources & Citations
Studies were read from their PubMed abstracts; the Prialt label (DailyMed version 6, effective May 31, 2025) was read October 6, 2026.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.