When someone overdoses, their body is overwhelmed by more of a substance than it can safely process. What happens next depends on the type of drug involved, but the most dangerous overdoses share a common endpoint: vital organs start shutting down. In 2024, 79,384 people in the United States died from drug overdoses, and roughly 60% of those deaths involved synthetic opioids like fentanyl.
How Opioid Overdoses Affect the Body
Opioids are the deadliest class of drugs when it comes to overdose, and breathing is the first thing to go. Opioids bind to receptors throughout the brainstem, the part of the brain that controls automatic breathing. When too many of these receptors are activated, the signals that tell your lungs to expand and contract become sluggish, then stop. Breathing slows from a normal rate of 12 to 20 breaths per minute down to just a few, or it stops entirely.
Once breathing fails, oxygen levels in the blood plummet. The brain, which consumes more oxygen than any other organ, is the first to suffer. Within minutes, brain cells begin dying from lack of oxygen in a process similar to what happens during a stroke. The heart, still beating but starved of oxygen, eventually develops irregular rhythms and can stop.
The classic signs of an opioid overdose are a triad: pinpoint pupils, slowed or absent breathing, and loss of consciousness. The person’s skin may turn blue or gray, especially around the lips and fingernails. Their body may go limp, and they may make gurgling or snoring sounds as their airway partially closes. Flushed skin or hives can also appear because opioids trigger histamine release.
How Stimulant Overdoses Differ
Cocaine and methamphetamine overdoses attack the body from the opposite direction. Instead of slowing everything down, stimulants flood the system with adrenaline-like signals that push the heart and brain into dangerous overdrive. Blood pressure spikes, body temperature soars, and the heart races erratically.
The cardiac damage is particularly severe. Stimulants alter the electrical signaling in the heart, disrupting its rhythm. In studies of people admitted for acute cocaine toxicity, 26% had dangerously prolonged electrical cycles in their heart, compared to just 4% of chronic users who weren’t in acute crisis. Methamphetamine shows a similar pattern: about a third of patients in one study had both a racing heart and prolonged electrical intervals, a combination that can trigger fatal cardiac arrest. Beyond rhythm problems, stimulants can cause coronary vasospasm (sudden narrowing of the arteries feeding the heart), heart attacks, and long-term weakening of the heart muscle.
A stimulant overdose often looks very different from an opioid one. The person may be agitated, confused, or seizing rather than unconscious. Their pupils are typically dilated. They may complain of chest pain, have a rapid pulse, or feel like their heart is pounding out of their chest. Dangerously high body temperature, sometimes above 106°F, can cause organ damage on its own.
Why Mixing Substances Is So Dangerous
Many overdose deaths involve more than one substance. When alcohol is combined with opioids or benzodiazepines (anti-anxiety medications like Xanax or Valium), the effects on the brain’s breathing centers multiply rather than simply adding together. All three of these substances suppress the central nervous system through related pathways, and combining even moderate amounts of two of them can be enough to stop breathing entirely. A person who could tolerate a certain dose of an opioid alone may overdose on the same amount if they’ve also been drinking.
Fentanyl has made this problem worse in a different way. Because it’s so potent, even tiny amounts mixed into counterfeit pills or other street drugs can push someone into an opioid overdose when they didn’t know they were taking an opioid at all.
Brain Damage in Survivors
Surviving an overdose doesn’t always mean a full recovery. Between 2016 and 2021, about 5% of people hospitalized for opioid overdose developed hypoxic-ischemic brain injury, the damage caused by the brain going without adequate oxygen. That number may sound small, but the consequences for those affected are severe.
The spectrum ranges widely. Mild cases involve difficulty thinking clearly, trouble finding words, or problems with memory. Severe cases can leave a person permanently unable to care for themselves, or in rare cases, result in complete loss of brain function. Among survivors with this type of brain injury, roughly 47% are discharged to skilled nursing facilities rather than home. Researchers estimate that about 65% of people who survive with oxygen-related brain injury will need significant ongoing medical care, and many will live with a high degree of disability.
What Happens in the First Minutes
The window between an overdose starting and becoming fatal can be very narrow, sometimes just a few minutes for potent synthetic opioids. Recognizing the signs quickly is the single most important factor in survival. For opioid overdoses, the key signs are unresponsiveness, slow or stopped breathing, and blue or gray skin. For stimulant overdoses, look for seizures, chest pain, extreme agitation, or loss of consciousness with a very fast pulse.
If you suspect an opioid overdose, naloxone (sold under the brand name Narcan) can reverse it. The nasal spray version is available without a prescription at most pharmacies. You place the nozzle in one nostril and press the plunger to deliver the full dose. If the person hasn’t responded after about three minutes, give a second dose in the other nostril. Naloxone only works on opioids, so it won’t help with a stimulant or alcohol overdose, but it also won’t cause harm if you’re unsure what the person took.
Regardless of the substance involved, call 911 immediately. Place an unconscious person on their side to keep their airway clear, and if they’re not breathing and you’re trained in CPR, begin rescue breathing. Even if naloxone revives someone, they still need emergency medical care because the drug wears off in 30 to 90 minutes, which is often shorter than the opioid itself lasts. The person can slip back into overdose after naloxone wears off.
Legal Protections for Calling 911
Fear of arrest is one of the most common reasons bystanders hesitate to call for help during an overdose. Most states have addressed this with Good Samaritan overdose prevention laws, which provide some form of legal protection to people who call 911 to report an overdose. The specifics vary by state. Some offer broad immunity from drug-related criminal charges for both the caller and the person overdosing. Others treat calling for help as a mitigating factor during sentencing rather than full immunity. These laws have been enacted across all 50 states and Washington, D.C., though the scope of protection differs. Knowing your state’s version can remove the hesitation that costs lives.