What Is Ziconotide (Prialt)? The Cone Snail Peptide for Severe Chronic Pain and What Its Trials Found

Ziconotide, sold as Prialt, is a pain medicine that began as venom. It is a synthetic copy of a peptide made by Conus magus, a fish hunting marine cone snail, and the [FDA label on DailyMed](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b025d8ed-937d-4597-9ad1-0b2f6e0ee5b1) lists an initial U.S. approval in 2004. You will not find ziconotide as a pill or a shot, because it is infused directly into the fluid around the spinal cord through an implanted pump, and it is reserved for adults with severe chronic pain who have run out of other options, including intrathecal morphine.

Ziconotide matters to anyone following peptide research because it is one of the few nonopioid drugs for severe pain that made it all the way through approval. A 2019 review by cone snail researchers at the University of Utah ([Safavi-Hemami, Journal of Proteomics, 2019](https://doi.org/10.1016/j.jprot.2018.05.009)) notes that most attempts to develop nonopioid drugs for severe pain have failed, and it calls ziconotide "a notable exception." This article covers how the peptide works, what its three placebo controlled trials found, how it is dosed and what its label says about the real risks. It is educational content about published research, not medical advice.

Ziconotide comes from the venom of Conus magus, a cone snail that hunts fish by injecting a cocktail of paralyzing peptides. The Prialt label describes the drug as "a synthetic equivalent of a naturally occurring conopeptide found in the piscivorous marine snail, Conus magus."

Cone snail venom peptides, called conotoxins or conopeptides, evolved to shut down a prey animal's nervous system very quickly. Each species produces many different peptides, and each one is aimed at a specific ion channel or receptor, which is exactly the kind of precision drug developers look for. The peptide behind ziconotide hits one type of calcium channel that nerves use to pass pain signals along.

The University of Utah review frames ziconotide as proof of a larger idea, that cone snail venoms can supply a steady pipeline of leads for nonopioid pain drugs, with other Conus peptides now in clinical or preclinical development. Among those venom peptides, ziconotide remains the one that reached FDA approval for pain.

Ziconotide works by blocking N-type calcium channels on the nerves that carry pain signals into the spinal cord. According to the label, it binds these channels on primary nociceptive (A-delta and C) afferent nerves in the superficial layers of the dorsal horn, known as Rexed laminae I and II.

When a pain signal reaches the end of one of these nerves, calcium flows in through N-type channels and triggers the release of excitatory neurotransmitters onto the next nerve in the chain. Blocking the channel blunts that handoff, so less of the signal travels up to your brain. The label is careful on this point, stating that the mechanism "has not been established in humans" and that the description comes from animal research.

Ziconotide is not an opioid and does not act on opioid receptors, which is why the label states that it can be "interrupted or discontinued abruptly without evidence of withdrawal effects." The flip side is that ziconotide does nothing to prevent opioid withdrawal, so the label warns that patients must not be abruptly withdrawn from opiates when ziconotide is started.

Ziconotide is a small, tightly folded peptide. The label lists it as a 25 amino acid, polybasic peptide containing three disulfide bridges, with a molecular weight of 2639 daltons. Those three disulfide bridges lock the chain into a rigid knot, a shape that is typical of conotoxins and part of the reason the molecule fits its channel target so precisely.

Ziconotide is given intrathecally, into the cerebrospinal fluid around the spinal cord, because that is where its target sits and because a peptide like this one cannot simply be swallowed. The label calls for a sterile, preservative free solution delivered with "an appropriate microinfusion device," which in practice is usually a pump implanted under the skin with a catheter running into the spinal canal.

Once ziconotide is in the spinal fluid, it does not last long. The label gives a CSF half life of about 4.6 hours and a serum half life of 1.3 hours, and within 24 hours of stopping, the CSF concentration should fall below 5% of peak. That short half life is why ziconotide is delivered as a continuous infusion, and it is also why side effects can usually be reversed fairly quickly by turning the pump down or off.

The intrathecal route carries its own risks. The label warns about meningitis and other infections and asks patients, caregivers and clinicians to watch for signs such as fever, headache, stiff neck and confusion.

Three randomized, double blind, placebo controlled trials support ziconotide, and together they tell a story about dosing as much as about pain relief. The first two used fast titration to high doses and showed large effects alongside heavy side effects, while the third used slow titration to a low dose and showed a smaller effect that patients tolerated better.

Staats 2004, cancer and AIDS pain. The first of the three trials ([Staats, JAMA, 2004](https://doi.org/10.1001/jama.291.1.63)) enrolled 111 people with cancer or AIDS at 32 centers, each with a baseline pain score of 50 mm or higher on a 100 mm scale. Patients were randomized 2:1 to ziconotide or placebo, titrated over 5 to 6 days, and they were people with heavy pain, since 98.5% of the ziconotide group was already taking opioids. Mean pain scores improved 53.1% on ziconotide versus 18.1% on placebo, moderate to complete relief was reported by 52.9% versus 17.5%, and five patients on ziconotide had complete pain relief. The authors concluded that intrathecal ziconotide "provided clinically and statistically significant analgesia."

Wallace 2006, chronic pain not caused by cancer. The second trial ([Wallace, Neuromodulation, 2006](https://doi.org/10.1111/j.1525-1403.2006.00055.x)) enrolled 255 people (169 on ziconotide, 86 on placebo) with severe chronic nonmalignant pain that had not responded to conventional therapy, treated over 6 days in hospital. The starting dose was 0.4 mcg/hour with a maximum of 7.0 mcg/hour, but both were cut to 0.1 and 2.4 mcg/hour partway through because of adverse events. Mean pain reduction was 31.2% on ziconotide versus 6.0% on placebo, and the authors were frank that the rapid titration and high doses caused a considerable rate of side effects, including abnormal gait, dizziness, nausea, nystagmus, urinary retention and vomiting.

Rauck 2006, the slow titration trial. The third trial ([Rauck, Journal of Pain and Symptom Management, 2006](https://doi.org/10.1016/j.jpainsymman.2005.10.003)) tested the slower approach the label now uses. It randomized 220 people (112 on ziconotide, 108 on placebo) with severe chronic pain and an average baseline pain score of 80.7 out of 100. The infusion started at 0.1 mcg/hour and climbed gradually over 3 weeks, ending at a mean dose of 0.29 mcg/hour (6.96 mcg/day). Pain improved 14.7% on ziconotide versus 7.2% on placebo, a smaller but statistically significant gap, and the authors reported that slow titration to a low maximum dose "was better tolerated than in two previous controlled trials that used a faster titration to a higher mean dose."

The pattern across the three trials matters for how you read them. The faster, higher dose trials produced bigger average effects, but the label's dosing is built on the slow trial, because that is the one whose tolerability made the drug usable in practice.

Pooled analyses agree that ziconotide reduces pain and that it causes frequent side effects. A 2017 systematic review ([Brookes, Current Neuropharmacology, 2017](https://doi.org/10.2174/1570159x14666160210142056)) combined the three monotherapy trials and found a pooled odds ratio of 2.77 (95% CI 1.37 to 5.59) for responding on ziconotide versus placebo, while also noting methodological issues that "may call into question the validity of the results."

The largest analysis to date ([Picañol, Pain Reports, 2025](https://doi.org/10.1097/PR9.0000000000001363)) covered 23 studies and 1,531 participants. Ziconotide lowered pain intensity compared with placebo (mean difference of 22.54 points), although results varied widely between studies. Adverse events were reported in 94.9% of ziconotide patients versus 76.9% on placebo (risk ratio 1.24), and serious adverse events occurred in 17.85% (risk ratio 2.63).

The 2025 review also asked whether ziconotide lets patients cut back on opioids. Observational studies reported decreases ranging from 6.4% to 91.5%, but "randomized trials showed inconsistent results," and the authors rated the overall certainty of evidence as low to moderate and called for cautious use.

Ziconotide is dosed in micrograms per day through the pump, and the label's rule is to start low and climb slowly. Dosing begins at no more than 2.4 mcg/day (0.1 mcg/hr) and can be raised by up to 2.4 mcg/day, no more than 2 to 3 times per week, up to a recommended maximum of 19.2 mcg/day (0.8 mcg/hr) by Day 21. The label lists two vial strengths, 25 mcg/mL and 100 mcg/mL.

The gap between the recommended ceiling and what was once tested shows why the slow approach won out. According to the label, the maximum intrathecal dose given in clinical trials was 912 mcg/day, far above the current recommended maximum of 19.2 mcg/day, and people who received doses above the recommended maximum had exaggerated effects such as ataxia, nystagmus, dizziness, stupor and confusion. There is no known antidote, and the label notes that most patients recovered within 24 hours after the drug was stopped.

Expert reviewers describe ziconotide as having a narrow therapeutic window. A 2019 review in Pain Medicine ([Deer, Pain Medicine, 2019](https://doi.org/10.1093/pm/pny132)) notes that ziconotide "requires careful dose titration" and that a trial period is recommended before a patient commits to a pump.

The most common side effects of ziconotide are neurological, led by dizziness, nausea, confusion and abnormal eye movements. The label's table from the slow titration trial (112 patients on ziconotide, 108 on placebo) gives the clearest picture, because it reflects the dosing approach now in use.

Across the full development program, 1254 adults received ziconotide, adding up to 662 patient years of exposure. The mean treatment duration was 193 days, and 173 patients (14%) were treated for at least a year.

The label also flags a lab finding you would not expect from a pain drug. In clinical studies, 40% of treated patients had creatine kinase (CK), a muscle enzyme, above the upper limit of normal, and 11% had levels more than three times that limit, so the label recommends checking serum CK periodically during treatment.

Ziconotide carries a boxed warning because it can cause severe psychiatric symptoms and neurological impairment. The label states that patients with a preexisting history of psychosis must not be treated with it, and it asks clinicians to monitor all patients frequently for cognitive impairment, hallucinations and changes in mood or consciousness.

The label lists the psychiatric events seen in trials, including hallucinations (12%), paranoid reactions (3%), hostility (2%), delirium (2%) and psychosis (1%). It also states that ziconotide may cause or worsen depression, with a risk of suicide in susceptible patients, and that in placebo controlled trials, suicide, suicide attempts and suicidal ideation ran at 0.27 per patient year on ziconotide versus 0.10 per patient year on placebo.

Clinicians in Germany ([Maier, Pain, 2011](https://doi.org/10.1016/j.pain.2010.10.007)) reported two cases that raised the suspicion that ziconotide had triggered suicidality, including one in a patient with no depressive symptoms at the start. Two case reports cannot prove cause, but the authors concluded that a comprehensive psychiatric evaluation is needed before and during treatment. Because ziconotide's half life is short and it has no withdrawal syndrome, the pump can be stopped quickly when psychiatric symptoms appear.

Ziconotide and morphine are the two drugs most often placed first in an intrathecal pump, and they carry different kinds of risk. The 2016 Polyanalgesic Consensus Conference (PACC) guidelines, as summarized by Deer and colleagues in Pain Medicine (2019), recommended both as first line intrathecal monotherapy for cancer and noncancer pain, with one consensus point favoring ziconotide first in chronic noncancer pain unless it is contraindicated.

The trade off is easy to see once the two are side by side. Intrathecal morphine brings the familiar opioid risks of dose increases, dependence and respiratory depression, while ziconotide avoids those but demands slow titration and close psychiatric monitoring. The Deer review stresses that the first drug in the pump should depend on the individual patient, including their psychiatric history.

Ziconotide is a prescription drug given only through implanted intrathecal pumps by specialist pain teams, and it has no sensible use outside that setting. Its label demands a sterile, preservative free solution, a dedicated microinfusion device, slow titration and close monitoring for infection, CK changes and psychiatric symptoms, none of which translates to a vial and a syringe at home.

If you are interested in research peptides more broadly, ziconotide is a useful reference point. It shows what it took for a venom peptide to become a medicine, from three controlled trials to a dosing scheme rebuilt after the first two caused too many side effects, and it is a reminder that peptides acting on the nervous system can carry serious psychiatric effects. For a primer on the basics, see our guide to [peptide side effects](/articles/peptide-side-effects-beginners) and our [peptide safety guide](/articles/peptide-safety-guide-women).

Ziconotide is a genuine success story for venom peptide research, because a cone snail toxin became an FDA approved, nonopioid treatment for people whose severe pain has outlasted every other option. Its trials show real pain relief, but the size of the benefit fell as the dosing became gentler, and even at the slow titration used today, dizziness, nausea, confusion and psychiatric effects are common enough to require close specialist monitoring. If you take one lesson from Prialt, let it be that a peptide powerful enough to quiet pain signals in the spinal cord also needs careful dosing, a sterile delivery system and a team watching for side effects.