Succinylcholine is a fast-acting muscle relaxant used in emergency and surgical settings to temporarily paralyze skeletal muscles. It takes effect within 60 seconds of injection and wears off in about 6 to 10 minutes, making it one of the quickest and shortest-acting paralytic drugs available. Its speed is the reason it remains a go-to choice when doctors need to insert a breathing tube rapidly.
How Succinylcholine Works
Your muscles contract when a chemical messenger called acetylcholine attaches to receptors at the junction between nerves and muscle fibers. Succinylcholine mimics acetylcholine: it binds to those same receptors and initially stimulates the muscle. This is why patients often experience visible muscle twitching, called fasciculations, immediately after receiving the drug. In studies, about 95% of patients who received succinylcholine without any pretreatment developed these brief, involuntary muscle twitches.
After that initial burst of stimulation, the drug keeps the receptors occupied and prevents them from resetting. The muscle can no longer respond to nerve signals, and temporary paralysis sets in. Unlike the body’s natural acetylcholine, which is cleared almost instantly, succinylcholine lingers just long enough to block further contraction for roughly 6 minutes before your body’s enzymes break it down.
Why It’s Used
The main reason succinylcholine still sees widespread use is its unmatched combination of fast onset and short duration. When someone arrives in an emergency department and needs a breathing tube placed quickly, every second counts. This procedure, called rapid sequence intubation, requires the jaw and vocal cords to be completely relaxed so the tube can pass into the airway without resistance. Succinylcholine reliably achieves that in under a minute.
A large Cochrane review comparing succinylcholine to rocuronium, the most common alternative, found that succinylcholine produced superior intubating conditions overall. Rocuronium can achieve comparable results at higher doses, but it lasts 37 to 72 minutes, meaning a patient remains paralyzed far longer. That distinction matters: if the intubation attempt fails, a patient given succinylcholine will regain the ability to breathe on their own within minutes, while a patient given rocuronium will not. Rocuronium is generally reserved for patients who cannot safely receive succinylcholine.
How the Body Breaks It Down
An enzyme in the blood called pseudocholinesterase (also known as butyrylcholinesterase) is responsible for rapidly dismantling succinylcholine. This enzyme is produced in the liver and circulates in plasma, where it chops the drug into inactive pieces. The speed of this process is what gives succinylcholine its short duration.
Several conditions can reduce pseudocholinesterase levels and slow the drug’s breakdown. Liver disease, kidney disease, severe burns, malnutrition, pregnancy, heart failure, and certain cancers can all decrease the body’s production of the enzyme. Some chemicals and medications can also inhibit it directly, including organophosphate insecticides and certain antidepressants (MAO inhibitors). When pseudocholinesterase activity is low for any of these reasons, the paralysis from succinylcholine can last longer than expected.
Pseudocholinesterase Deficiency
Some people carry a genetic variation that makes their pseudocholinesterase enzyme defective or absent altogether. This condition is caused by changes in the BCHE gene and follows an autosomal recessive pattern, meaning you need to inherit one affected copy from each parent to have the full deficiency. People who carry just one copy may process the drug somewhat more slowly, with roughly a 30% increase in how long the paralysis lasts.
People with two affected copies face a dramatically different experience. Instead of the expected 6 to 10 minutes of paralysis, they can remain unable to move or breathe on their own for 2 to 3 hours. During that time, they need mechanical ventilation until the drug is eventually cleared. Most people with this deficiency have no idea they carry it until they receive succinylcholine for the first time. Genetic testing can identify the gene change, and anyone who has experienced prolonged paralysis after anesthesia (or has a family member who has) should be tested before future procedures.
Risks and Dangerous Reactions
The most significant risk of succinylcholine is a dangerous spike in blood potassium levels. When the drug stimulates muscle fibers during that initial phase of twitching, potassium flows out of muscle cells and into the bloodstream. In healthy people, this increase is small and harmless. But in patients with major burns, extensive trauma, prolonged immobility, or nerve damage, the number of receptors on muscle cells multiplies dramatically. When succinylcholine activates all of these extra receptors at once, the potassium release can be severe enough to stop the heart.
This risk typically peaks 7 to 10 days after the original injury and persists for an unpredictable period. Because of this, succinylcholine is strictly contraindicated after the acute phase of major burns, crushing injuries, extensive nerve damage, or upper motor neuron injuries like spinal cord trauma. It is also contraindicated in patients with certain inherited skeletal muscle diseases.
Malignant Hyperthermia
Succinylcholine is one of only two types of drugs known to trigger malignant hyperthermia, a rare but life-threatening reaction that occurs in genetically susceptible people. The condition causes muscles to enter an uncontrolled hypermetabolic state: body temperature skyrockets, muscles become rigid, and the body produces dangerous levels of acid and carbon dioxide. It affects roughly 1 in 100,000 adults and 1 in 30,000 children, and carries a mortality rate of 3% to 5% even with proper treatment.
Malignant hyperthermia is inherited in an autosomal dominant pattern, so a single copy of the affected gene is enough to put someone at risk. Treatment requires immediate administration of a specific drug called dantrolene, which works by blocking abnormal calcium release inside muscle cells. Because of this risk, many outpatient surgical facilities choose not to stock succinylcholine at all, since carrying the drug also requires stocking dantrolene, which is expensive. Anyone with a personal or family history of malignant hyperthermia should never receive succinylcholine.
Fasciculations and Muscle Soreness
The muscle twitching that accompanies succinylcholine is more than a visual curiosity. It can leave patients with noticeable muscle soreness the next day, similar to the feeling after an unusually intense workout. This postoperative myalgia is common enough that clinicians sometimes give a small dose of another type of muscle relaxant, or medications like lidocaine or magnesium, before the succinylcholine to dampen the fasciculations. These pretreatments are effective, with studies showing they can prevent fasciculations in the vast majority of patients.
How It Compares to Alternatives
No other paralytic drug matches succinylcholine’s onset speed at standard doses. Rocuronium comes closest and is the most frequently used alternative, but the two drugs behave very differently after they take effect. Succinylcholine wears off on its own in minutes. Rocuronium, at standard doses, lasts 37 to 72 minutes and requires either waiting or administering a reversal agent to restore muscle function.
At higher doses of rocuronium (1.2 mg/kg), studies show no statistical difference in how well it relaxes the muscles for intubation compared to succinylcholine. The trade-off is always duration: choosing rocuronium means committing to a much longer period of paralysis. For emergency patients in whom succinylcholine is contraindicated, rocuronium still reliably creates acceptable intubating conditions, making it a solid backup rather than a first choice for most situations.