General anesthesia relies on several categories of drugs working together: one to make you unconscious, one to block pain, one to relax your muscles, and often an inhaled gas to keep you under throughout the procedure. No single drug does all of this alone. The anesthesiologist selects and combines these agents based on the type of surgery, your health, and how your body responds in real time.
Induction Agents: Drugs That Put You to Sleep
The first drug you receive is an intravenous induction agent, delivered through your IV to rapidly bring on unconsciousness. The three most common options are propofol, etomidate, and ketamine, and each has a distinct profile that determines when it gets used.
Propofol is by far the most widely used intravenous anesthetic in the world. It works by enhancing the activity of receptors in the brain that dampen neural signaling, essentially turning down electrical activity across your nervous system until consciousness fades. The tradeoff is that propofol lowers blood pressure, particularly in people who are dehydrated, elderly, or have weakened heart function. That drop is usually predictable and short-lived, and the dose can be adjusted to minimize it.
Etomidate shares a similar brain mechanism to propofol but is more hemodynamically stable, meaning it has less impact on blood pressure and heart rate. Emergency physicians often reach for it when a patient’s cardiovascular system is already under stress. One notable downside: etomidate can temporarily suppress the adrenal glands, which matters most in patients with severe infections or sepsis.
Ketamine works differently from the other two. Instead of boosting the brain’s inhibitory signals, it blocks a type of excitatory receptor, creating a dissociative state where you’re unconscious and pain-free. Ketamine typically raises blood pressure and heart rate slightly, which makes it useful for patients who are hemodynamically unstable. It’s a common choice in emergency and trauma settings for this reason.
Inhaled Anesthetics: Gases That Maintain Unconsciousness
Once you’re asleep, the anesthesiologist often switches to an inhaled gas delivered through a breathing tube or mask to keep you unconscious for the duration of surgery. These volatile agents are mixed with oxygen and flow continuously into your lungs, where they cross into the bloodstream and reach the brain within seconds.
The three volatile anesthetics used today are sevoflurane, desflurane, and isoflurane. Each requires a different concentration to maintain anesthesia. Desflurane requires the highest concentration (around 6.6%), sevoflurane needs roughly 2.0 to 2.6%, and isoflurane falls in between at about 1.2 to 1.4%. All three reduce the volume of each breath you take, though the body compensates somewhat by increasing the breathing rate.
Sevoflurane is the most commonly chosen for the start of anesthesia because it has a mild smell and doesn’t irritate the airways. That makes it especially useful for patients with asthma, where it can actually help relax the airways. Desflurane and isoflurane, by contrast, have a pungent quality that can trigger airway spasm in sensitive patients, so they’re generally introduced only after the patient is already unconscious.
Nitrous oxide, sometimes called “laughing gas,” is an older agent still used as a supplement to other anesthetics. It’s not potent enough on its own to produce full anesthesia (you’d need a concentration of 104% to do so, which is physically impossible). Instead, it’s blended with other gases to reduce the amount of volatile anesthetic needed. One quirk: when nitrous oxide is turned off at the end of surgery, it floods out of the blood and into the lungs so quickly that it can temporarily displace oxygen from the air sacs. Anesthesiologists counter this by giving pure oxygen for several minutes after discontinuing it.
Opioids: Pain Control During Surgery
The induction agents and inhaled gases produce unconsciousness, but they don’t fully block the body’s pain response. Opioids fill that gap. The versions used during surgery are far more potent and shorter-acting than the opioids most people associate with pain pills.
Fentanyl is the most familiar surgical opioid and provides strong pain relief that lasts long enough for many procedures. Remifentanil is an ultra-short-acting alternative with a half-life of just 3 to 10 minutes, meaning its effects essentially vanish within minutes of stopping the infusion. That precision makes it ideal for procedures where the anesthesiologist needs to dial pain control up and down quickly in response to changing surgical intensity. Sufentanil is another option with a potency and duration between the two.
Muscle Relaxants: Enabling Intubation and Surgery
Many surgeries require your muscles to be completely still, and placing a breathing tube also requires the muscles of the throat and vocal cords to go slack. Neuromuscular blocking agents accomplish this by interrupting the chemical signals between nerves and muscles.
These drugs fall into two categories. The depolarizing type, represented by succinylcholine, initially activates muscle receptors all at once (which can cause brief, visible twitching called fasciculations) and then leaves the muscles unable to fire again. Succinylcholine kicks in within about a minute and wears off in 7 to 12 minutes, making it the go-to choice when the anesthesiologist needs rapid, brief paralysis to place a breathing tube quickly.
Nondepolarizing agents like rocuronium and vecuronium take a different approach. They sit on the muscle receptors and block the body’s own signaling molecule from landing, so the muscles never receive the instruction to contract. These drugs last longer than succinylcholine and are used to maintain relaxation throughout surgery. The duration varies by drug and dose, ranging from roughly 20 minutes to over an hour.
Reversing Muscle Relaxants
At the end of surgery, any lingering muscle paralysis needs to be reversed before you can breathe on your own and have your breathing tube removed. Two reversal agents are in common use. Neostigmine is the older option, working by increasing the concentration of the body’s own signaling molecules at the muscle receptor so they can outcompete the blocking drug. It takes an average of about 18.6 minutes to fully restore muscle strength.
Sugammadex is a newer drug that works completely differently: it physically wraps around and traps the muscle relaxant molecule, pulling it out of circulation. Recovery to full muscle strength takes roughly 1.5 minutes. That speed and predictability have made sugammadex increasingly preferred, though neostigmine remains widely used because of its lower cost and decades of clinical experience.
Premedications and Supportive Drugs
Before anesthesia even begins, you may receive several additional medications. A short-acting sedative from the benzodiazepine family is commonly given to ease anxiety in the preoperative area. These drugs also work through the same inhibitory brain receptors as propofol and etomidate, producing calm and mild amnesia for the period around surgery.
Anti-nausea medication is frequently given preventively, since both anesthetic gases and opioids are well-known triggers for postoperative nausea and vomiting. A drug to reduce saliva and airway secretions may also be administered, which helps keep the airway clear during intubation.
Total Intravenous Anesthesia: Skipping the Gas
In some cases, the anesthesiologist avoids inhaled gases entirely and maintains anesthesia using only intravenous drugs. This approach, called total intravenous anesthesia (TIVA), most commonly pairs a continuous propofol infusion with remifentanil. Because both drugs are short-acting and precisely controllable, the anesthesiologist can fine-tune the depth of anesthesia minute by minute.
TIVA is gaining popularity for several reasons. It produces less postoperative nausea and vomiting compared to inhaled anesthetics, which makes it especially attractive for patients prone to that problem. It also eliminates the risk of operating room contamination with anesthetic gases. In studies comparing TIVA to inhaled techniques during abdominal surgery, the IV approach was associated with less intraoperative bleeding, fewer complications, shorter hospital stays, and higher surgeon satisfaction with operating conditions. TIVA is also the standard choice for certain neurosurgeries and for patients with a rare genetic susceptibility to a dangerous reaction triggered by volatile anesthetics.
How These Drugs Work Together
The concept behind modern general anesthesia is “balanced anesthesia,” using lower doses of several drug types rather than a high dose of any single one. Each class targets a different piece of the puzzle: unconsciousness, pain suppression, muscle relaxation, and suppression of the body’s stress reflexes. By combining them, the anesthesiologist achieves a deep, stable anesthetic state while minimizing the side effects that would come from pushing any one drug to a high dose. The specific combination is tailored to you, your medical history, and what the surgery demands.