What Are the Most Common Butorphanol Side Effects?

Butorphanol’s most frequently reported side effects are drowsiness, dizziness, and nausea or vomiting, regardless of whether it is given by injection or nasal spray.¹ Those three reactions dominate the clinical picture, but butorphanol also produces a distinct pattern of mood and perception changes that sets it apart from more familiar opioids such as morphine. Understanding the full range of effects, and why they happen, helps make sense of both the drug’s clinical niche and its limitations.

The Three Side Effects You Are Most Likely to Notice

Dizziness, drowsiness, and nausea show up in study after study as the leading complaints. In a migraine trial using the nasal spray, about 58 percent of patients reported dizziness (compared with 4 percent on placebo), roughly 38 percent had nausea or vomiting, and 29 percent felt drowsy.² Those numbers are high, but they were partly tangled up with the migraine itself, which already causes nausea and light-headedness. Even so, the pattern is consistent across different clinical settings: dizziness tends to be the single most common reaction, with drowsiness close behind.

A study of patients undergoing combined gastroscopy and colonoscopy found that dizziness rates climbed steeply with dose. At the highest dose tested, 64 percent of patients experienced dizziness, compared with 38 percent at lower doses. Drowsiness followed a similar trend, reaching 13 percent at the top dose versus 3 to 5 percent in the lower-dose groups.³ The practical takeaway is that these effects are dose-dependent: lower doses still work for pain or sedation but carry noticeably less dizziness and sleepiness.

Dysphoria, Confusion, and the Kappa-Opioid Connection

If you have ever heard someone describe a “weird” or “unpleasant” feeling after butorphanol, there is a pharmacological reason for it. Unlike morphine and most other common opioids, which primarily activate the mu-opioid receptor and tend to produce feelings of euphoria, butorphanol has roughly 20-fold greater affinity for the kappa-opioid receptor.⁴ Kappa activation is what causes the dysphoria, the foggy or unsettled mood, and the confusion that some people report. In a study comparing butorphanol with morphine in experienced opioid users, volunteers given butorphanol reported dysphoria, confusion, and heavy sedation, while morphine produced the expected euphoria and mild stimulation.⁵

This difference matters in two ways. First, the dysphoric quality makes butorphanol less rewarding than most opioids, which is one reason some clinicians consider it somewhat lower risk for misuse, though “lower risk” is not the same as “no risk.” Second, if you are prescribed butorphanol and feel anxious, disconnected, or emotionally flat afterward, that reaction is a recognized pharmacological effect of kappa activation, not a sign that something has gone dangerously wrong. It usually fades as the drug wears off.

How the Route of Administration Shapes Side Effects

Butorphanol is available as an injectable (intravenous or intramuscular) and as a nasal spray. The overall side-effect profile is largely the same between the two routes.⁶ What changes is timing and intensity. The nasal spray is absorbed through the mucous membranes and reaches the bloodstream quickly, so side effects tend to set in within minutes and feel more abrupt. The injectable form given intravenously has an even faster onset, but it is administered in a medical setting where drowsiness and dizziness are expected and monitored.

The nasal spray became associated with misuse in the 1990s and early 2000s partly because it was easy to use outside a clinic and could be re-dosed without supervision. That self-dosing pattern amplified the side effects: more frequent sprays meant more sedation and more dizziness, plus a steeper climb toward tolerance. Most of the serious adverse event reports for butorphanol have involved the nasal formulation used beyond the prescribed schedule.

Respiratory Depression and the Ceiling Effect

One of butorphanol’s selling points compared with full mu-agonist opioids is its respiratory ceiling effect. Because it acts as a partial agonist at certain receptor pathways, increasing the dose past a certain point does not keep pushing breathing rate further down the way morphine or fentanyl can. This does not mean there is zero respiratory risk. Butorphanol can depress breathing, especially at higher doses, in people with pre-existing lung disease, or when combined with other central nervous system depressants like benzodiazepines or alcohol.

In a labor analgesia study, women who received butorphanol experienced sedation that sometimes lasted longer than expected, but none required an antidote or respiratory support.⁷ That is a typical clinical experience: meaningful respiratory depression from butorphanol alone is uncommon in healthy people at standard doses, but it remains possible and warrants monitoring.

Cardiovascular Effects

Butorphanol can lower blood pressure and heart rate. In clinical use, these changes are usually small enough to go unnoticed by the patient, but they can become relevant during general anesthesia or in people whose blood pressure is already on the low side. Most of the detailed cardiovascular data on butorphanol comes from veterinary anesthesia research, which has studied the question more systematically than the human literature.

In dogs anesthetized with desflurane, butorphanol caused a drop in mean arterial pressure from about 86 mmHg down to 64 mmHg, a clinically meaningful decrease even though cardiac output was maintained.⁸ In horses under isoflurane anesthesia, the cardiovascular picture was more reassuring: blood pressure and heart rate did not change in most cases, though decreases in blood pressure were seen in animals under deeper anesthesia planes.⁹ The takeaway for human patients is that butorphanol alone is unlikely to cause dangerous cardiovascular events in a healthy person, but combining it with anesthetic agents or sedatives can amplify its blood-pressure-lowering effect.

Tolerance, Cross-Tolerance, and Dependence

Butorphanol can produce physical dependence, and tolerance develops with repeated use. Its kappa-receptor activity plays a key role in how that tolerance forms and in the somewhat unusual cross-tolerance pattern it creates with other opioids.¹⁰

Animal studies have mapped this out in detail. In rats maintained on low-dose butorphanol, tolerance developed to butorphanol itself and to lower-efficacy mu-opioid drugs like buprenorphine and morphine, but not to high-efficacy ones like fentanyl and sufentanil. At higher maintenance doses, tolerance spread to all the tested mu-opioids.¹¹ Interestingly, the cross-tolerance does not always go both ways. In mice treated chronically with morphine, butorphanol’s pain-relieving effects were not reduced, even though morphine tolerance had clearly developed. In contrast, chronic treatment with buprenorphine did reduce the effect of morphine, while butorphanol did not.¹²

What this means practically is that someone who has been taking butorphanol regularly may not get the same pain relief from certain other opioids, and the degree of that cross-tolerance depends on how much butorphanol they have been using. Conversely, someone already tolerant to morphine may still respond to butorphanol, because butorphanol’s analgesic action draws substantially from the kappa receptor rather than relying entirely on mu pathways. This asymmetry is part of what makes butorphanol pharmacologically interesting, but it also complicates pain management when switching between opioids.

What Happens If You Take Too Much

Butorphanol’s side effects, including somnolence, dizziness, nausea, and even a case of motor impairment called apraxia, are reversible with naloxone, the same opioid antagonist used for morphine and fentanyl overdoses.¹³ In one reported case, a woman who had accidentally overused the nasal spray and lost coordinated movement recovered completely after a single intramuscular dose of naloxone. Because butorphanol’s effects plateau to some extent at higher doses (the ceiling effect), the window between a therapeutic dose and a life-threatening overdose is wider than it is for full mu-agonist opioids. Still, mixing butorphanol with alcohol, benzodiazepines, or other sedatives narrows that margin considerably.

Use During Labor and Effects on Newborns

Butorphanol is used in some obstetric settings as an alternative to epidural anesthesia for labor pain. In prospective studies, newborn health scores assessed at one and five minutes after birth did not show adverse effects from the mother’s butorphanol use, and no newborn respiratory depression was reported.¹⁴ Another study described the incidence of adverse outcomes as low, concluding that butorphanol can be given with reasonable safety for both mother and baby.¹⁵

The main maternal side effect in labor is prolonged sedation. Some women stayed drowsy longer than anticipated, which is not dangerous in a monitored setting but can interfere with the early bonding and breastfeeding window. If you are considering butorphanol for labor analgesia, the tradeoff is real pain relief versus the possibility of being groggier than you would like during the first hours with your baby.

Interactions with Other Sedating Drugs

Combining butorphanol with other drugs that depress the central nervous system amplifies its sedative and cardiovascular effects. Veterinary research has documented this particularly well. When butorphanol was given alongside the sedative acepromazine in dogs, heart rate dropped further than with either drug alone, and breathing rate also decreased.¹⁶ The same principle applies in humans: adding a benzodiazepine, a muscle relaxant, alcohol, or another opioid to butorphanol can push sedation into territory where breathing and blood pressure fall to dangerous levels.

There is also an important interaction in the other direction. Because butorphanol is a partial agonist at the mu receptor, it can partially block the effect of a full mu-agonist given at the same time. If someone on chronic morphine or hydrocodone therapy receives butorphanol, it could precipitate withdrawal symptoms by competing for the mu receptor without activating it as strongly. This is the same mechanism that makes buprenorphine tricky to start in opioid-dependent patients. In practice, butorphanol is generally avoided in people already on high-dose mu-agonist opioids.

Butorphanol in Veterinary Medicine

Butorphanol is widely used in veterinary practice across species, and its side-effect profile in animals echoes many of the same themes seen in humans but with a few species-specific quirks. In dogs, a combination of alfaxalone and butorphanol produced moderate sedation along with tremors, involuntary eye movements, and heightened sensitivity to sounds.¹⁷ Those sensory side effects (nystagmus and auditory hyperesthesia) are rarely reported in humans, but they can be distressing in animals and are worth knowing about if you are a pet owner whose animal is receiving this drug.

In cats, butorphanol has been associated with dysphoria, echoing the same kappa-driven mood disturbance seen in people.¹⁸ Cats receiving butorphanol alone showed signs of distress or agitation that did not appear with hydromorphone or with a hydromorphone-butorphanol combination. In birds, the picture is more encouraging: combined butorphanol and midazolam premedication in psittacine species (parrots and their relatives) appeared safe and allowed lower doses of anesthetic gas to be used during procedures.¹⁹

How Butorphanol Compares with Other Opioids in Surgical Settings

In perioperative settings, butorphanol and drugs in a similar class (mixed agonist-antagonists like nalbuphine) have been studied for their ability to prevent catheter-related bladder discomfort and emergence agitation, two common postoperative problems. A randomized trial in patients who had open spinal surgery found that both butorphanol and nalbuphine reduced these complications without significant adverse events.²⁰ The advantage here is that butorphanol controls agitation and discomfort while carrying a lower risk of the respiratory depression that full mu-agonists would pose in the immediate post-surgical window.

Where butorphanol falls short is in treating severe, ongoing pain. Its partial agonist ceiling limits how much analgesia it can deliver, and the dysphoria can make patients feel worse even when the pain itself is controlled. For major trauma, post-surgical pain from large procedures, or cancer pain, full mu-agonists remain the standard despite their own side-effect baggage. Butorphanol tends to be most useful in episodic, moderate pain situations: migraine, procedural sedation, labor, and short-term post-operative discomfort.

The Dependence Question

Because butorphanol produces dysphoria rather than euphoria, early marketing sometimes characterized it as having low abuse potential. That turned out to be overly optimistic. The nasal spray formulation in particular became subject to patterns of escalating use, with patients spraying more frequently than prescribed to manage rebound symptoms. The dysphoric quality may make casual recreational use less appealing, but physical dependence still develops with regular dosing, and withdrawal can include anxiety, irritability, insomnia, sweating, and flu-like symptoms similar to those seen with other opioids.²¹

The fact that butorphanol is a Schedule IV controlled substance in the United States (compared with Schedule II for morphine and oxycodone) reflects the judgment that its abuse liability is lower, not absent. If your doctor prescribes a short course of butorphanol nasal spray for migraines, the risk of developing dependence from occasional, as-directed use is small. The risk climbs if you start using it daily, re-dosing more frequently than prescribed, or combining it with other substances to offset the dysphoria.

Side Effects in Older Adults and People with Liver or Kidney Problems

Butorphanol is metabolized primarily by the liver and excreted partly through the kidneys. In people with significant liver impairment, clearance slows down, meaning the drug sticks around longer and side effects like drowsiness and dizziness are more pronounced and more prolonged. Standard prescribing practice calls for a longer interval between doses in these patients rather than a lower individual dose, though clinicians sometimes do both.

Older adults are more sensitive to butorphanol’s sedative and blood-pressure-lowering effects for the usual reasons: reduced kidney and liver function, lower body water, and greater sensitivity of the central nervous system to opioids in general. The dizziness, in particular, raises fall risk in elderly patients, and falls in this population can lead to fractures and hospitalizations. If you are over 65 or caring for someone who is, extra caution with dosing and monitoring is warranted.

There is less formal guidance on butorphanol in people with kidney disease specifically, but because any drug that is partly renally cleared will accumulate in kidney impairment, the same principle applies: lower doses or longer intervals, with careful attention to sedation levels.