If you have ever heard someone say, “Anesthesia made me really sick” or “I woke up so slowly,” you may wonder why anesthesia affects people differently. Even with the same medicine or dose, anesthesia is not one-size-fits-all.
Small differences can influence breathing, heart rate, pain control, nausea and how quickly you wake up. Your anesthesiologist uses your health history, medications, airway, past reactions and procedure type to build a plan that helps keep you safe and comfortable.
“We’re not just giving a drug and stepping back. We’re continually monitoring the patient, much like a pilot flies a complex aircraft. Modern anesthesia is really a dynamic, moment-to-moment balancing act between keeping you unconscious and pain-free on one side and keeping your physiology stable on the other,” said Samuel Galvagno, DO, an anesthesiologist with Banner - University Medicine.
Why does anesthesia affect people differently?
“This is one of the most fascinating aspects of our field. Part of it is pharmacokinetics, which is how your body absorbs, distributes and eliminates the drug. Part of it is pharmacodynamics, which is how sensitive your brain and tissues are to the drug’s effect and what the drug is doing to your body,” Dr. Galvagno said.
Factors that can affect anesthesia include:
- Age
- Body size and body composition
- Genetics
- Liver and kidney function
- Heart or lung disease
- Sleep apnea
- Airway anatomy
- Medications and supplements
- Alcohol, marijuana, nicotine or other substance use
- Pain tolerance and opioid tolerance
- Prior anesthesia reactions
- Anxiety or past medical trauma
Genetics and anesthesia: Does red hair really matter?
Some research suggests people with natural red hair may need slightly more of certain anesthetic medicines. This is linked to variation in the MC1R gene, which affects hair pigment as well as pain and anesthesia response. It doesn’t mean anesthesia is unsafe for redheads.
Why sleep apnea matters before anesthesia
Sleep apnea can affect anesthesia because when you’re sedated, your airway muscles relax. Plus, some pain medicines can slow your breathing. This can increase the risk of breathing problems during and after surgery.
Many people have sleep apnea and don't know it. Tell your anesthesiologist about these signs of sleep apnea before surgery:
- Loud snoring
- Breathing pauses during sleep
- Gasping or choking that wakes you up
- Daytime sleepiness
- Morning headaches
- High blood pressure with heavy snoring
- A CPAP or BiPAP prescription
- A planned sleep study
Substance use and anesthesia: Why honesty matters
Your anesthesia team is not judging you when they ask about substance use. Alcohol, marijuana, nicotine or other substances can affect sedation, breathing, heart rate, blood pressure, pain control, nausea and withdrawal risk.
- Alcohol use: Heavy alcohol use can increase risks related to withdrawal, bleeding, heart rhythm, liver function and healing. Stopping suddenly before surgery may be risky for some people.
- Marijuana, CBD and edibles: Cannabis use may affect how much anesthesia or sedation you need. Smoking marijuana can irritate the airway, while edibles, oils and CBD can affect sedation, heart rate, blood pressure or medication interactions.
- Nicotine, smoking and vaping: Smoking and vaping can affect your lungs and airway and nicotine can affect your heart rate, blood pressure and healing. Quitting or cutting back before surgery may help. Talk about the timing with your care team.
- Recreational drugs or non-prescribed substances: Stimulants, opioids, sedatives and other substances can affect anesthesia and recovery, so the anesthesia team needs to know what you used and when.
Medications and supplements that can affect anesthesia
Tell your anesthesiologist about all prescriptions, over-the-counter (OTC) medicines, vitamins and supplements you take. Some can affect bleeding, blood pressure, sedation, blood sugar or anesthesia interactions.
You may need to pause or adjust some medications before surgery but don’t stop taking anything unless your health care team recommends that you do.
Previous anesthesia reactions and side effects
Tell your anesthesiologist if you or a family member had:
- Nausea
- Trouble waking up
- Breathing problems
- Difficult intubation
- Allergic reactions
- Awareness under anesthesia
- Any family history of malignant hyperthermia
- Unexplained death or serious reaction during surgery in a family member
“A family history of anesthesia reactions matters enormously,” Dr. Galvagno said.
What is malignant hyperthermia?
Malignant hyperthermia is a rare inherited reaction to certain anesthesia medicines. Tell your anesthesiologist if you or a family member has had a high fever, rigid muscles or a severe reaction during surgery.
If you’re at risk, the anesthesia team can avoid triggering medicines and use safer alternatives.
Airway differences and anesthesia breathing tube planning
Your anesthesiology team may need to support your breathing or place a breathing tube. They will consider factors like obesity, body composition and neck size.
Tell your anesthesiologist about:
- Loose teeth
- Dental work
- Jaw problems
- Neck stiffness
- Past airway difficulty
This information helps your care team choose the right tools, positioning and backup plans to help keep you safe.
Anxiety, panic and past medical trauma
“High baseline stress hormones can alter drug responses in ways we have to anticipate,” Dr. Galvagno said.
Tell your anesthesiologist if you have panic attacks, fear of needles, claustrophobia, past medical trauma or other behavioral health conditions. This can help them plan your sedation, anxiety support and recovery care.
Why did I feel sick after anesthesia before?
Nausea and vomiting can happen after anesthesia based on your history, procedure type, sex, motion sickness, migraine history, nonsmoking status and pain medicines.
If it happened before, tell your anesthesiologist. Your care team can plan medicines to lower your risk.
What your anesthesiologist needs to know before surgery
“Everything. We mean that sincerely. Patients sometimes downplay things they think are embarrassing or irrelevant, like recreational drug use, supplements or how much they really drink. But all of it matters,” Dr. Galvagno said.
Tell your anesthesiologist about:
- Medical conditions
- Sleep apnea
- Medications
- Supplements
- Substance use
- AllergiesPast anesthesia reactions
- Family history of issues with anesthesia
- Airway or dental concerns
It’s common to meet your anesthesiologist right before surgery. “However, if you have significant medical history, complex medications or prior anesthesia problems, ask to speak with someone from the anesthesia team in advance. You deserve that conversation,” Dr. Galvagno said.
The goal: Safer anesthesia and smoother recovery
Your anesthesiologist uses your health history, medications, risk factors and real-time monitoring to personalize anesthesia and help you stay safer.
Bottom line
Anesthesia affects people differently because every body responds to medicine in its own way. Being honest with your anesthesiologist helps them personalize your care, reduce risks and support a smoother recovery.
If you’re planning surgery or a medical procedure, reach out to a Banner Health provider to learn more about how anesthesiology works as part of your overall plan.
Frequently asked questions about anesthesia
Why does anesthesia affect people differently?
Genetics, metabolism, medical conditions, medications, sleep apnea, airway anatomy, substance use and past anesthesia reactions can change how the body responds.
Does red hair really change anesthesia?
Natural red hair may be linked with slightly higher anesthesia needs in some studies. Having red hair is not dangerous when you need anethesia but it is helpful information to share with your anesthesia team.
Can sleep apnea make surgery more dangerous?
Sleep apnea can increase breathing risks during and after anesthesia because sedation and pain medicines can relax the airway and slow breathing. Tell your team if you snore loudly, stop breathing during sleep or use CPAP.
Should I tell my anesthesiologist about marijuana use?
Yes. Tell your anesthesiologist about marijuana, CBD, edibles and other substances. They can affect anesthesia needs, breathing, heart rate, pain control and nausea.
Why did I feel sick after anesthesia before?
Post-anesthesia nausea can happen for many reasons, including your history, procedure type and pain medicines. Tell your anesthesiologist so they can plan prevention strategies.
What if I had trouble waking up after anesthesia?
Tell your anesthesia team. They will review what happened, your medications and your health history to plan a safer approach.
What should I bring to my anesthesia appointment?
Bring a medication and supplement list, allergy list, medical history, past anesthesia concerns, CPAP information if you use one and details about alcohol, nicotine, marijuana or other substance use.
Can anxiety affect anesthesia?
Anxiety can affect the surgery experience, pain, nausea, heart rate and recovery. Tell your anesthesiologist if you have panic attacks, needle fear, claustrophobia or past medical trauma.
