The body’s slow shutdown during substance overdose

In 2024, 5,565 deaths related to drug poisoning were registered in England and Wales, with opiates and opioids involved in almost half. In the same year, nearly 10,000 people in the UK died from alcohol. These deaths came at the end of a process that may have taken minutes or hours, during which the body struggled and failed to cope with a toxic dose. Knowing what that process looks like and how to interrupt it can help prevent overdoses and the resulting deaths.

What happens in the brain

Depressant substances, including alcohol, opioids, and benzodiazepines, work by altering how brain cells communicate. Alcohol enhances the effects of GABA, a chemical that tells your brain cells to slow down. At the same time, alcohol suppresses glutamate, a chemical that normally keeps brain cells active and alert. Opioids produce a similar slowing effect through different receptors, but with the same result.

When someone uses more drugs or alcohol than their body can process, this situation becomes overwhelming. Signals between brain cells drop off. Thoughts then become sluggish and consciousness begins to fade. The person may appear drowsy, confused, or completely unresponsive as the brain loses its ability to function.

Overdose and respiratory risks

The most dangerous effect of a depressant overdose is respiratory depression, a slowing or stopping of breathing caused by the substance’s effect on the brainstem. A 2020 study identified the precise location where this occurs, a small cluster of neurons called the preBötzinger Complex. This is where breathing rhythm originates.

The researchers found that just 70 to 140 neurons in this region are responsible for the brain’s sensitivity to opioids. This is a remarkably small number of cells controlling a function the body cannot survive without. That helps explain why an overdose can tip from survivable to fatal so quickly. When opioids or other depressants reach toxic levels, these neurons stop sending the signals that tell the lungs to breathe.

Breathing becomes slow and shallow, and gaps appear between breaths. The person may make snoring sounds as their airway relaxes and partially closes. In severe cases, breathing stops entirely. Without help, the body’s oxygen supply falls rapidly, affecting every organ.

The effects on the heart and circulation

The heart depends on oxygen to function. As oxygen levels drop, the heart slows, blood pressure falls, and blood can no longer deliver enough oxygen to the organs. This process can unfold over just a few minutes, and if the person has collapsed in an awkward position, the risk increases. A slumped posture can compress your chest or obstruct your airways, accelerating the decline even when the dose alone might not have been fatal.

In an alcohol overdose, alcohol’s direct action on the heart muscle and blood vessels makes it worse. At very high blood alcohol concentrations, usually above 0.35 percent, the heart and lungs become partially anaesthetised. A weakened heart, low blood pressure, and inadequate breathing create a cycle where each failing system makes the other ones worsen. Skin often becomes pale, cold, or clammy as blood flow retreats from your extremities toward the vital organs.

The effects on the organs

Starved of oxygen, the organs that depend on it most begin to suffer. Hypoxia, the medical term for insufficient oxygen reaching the body’s tissues, causes serious damage. This includes kidney failure, heart damage, seizures, nerve damage, stroke, and pneumonia from inhaling vomit.

Your brain is particularly vulnerable. It consumes a large amount of energy relative to its size and is “exquisitely sensitive to hypoxia”. Brain cells can start dying within minutes, and if the oxygen stays cut off, permanent damage can follow. Survivors of severe overdose sometimes experience lasting problems with memory, thinking, or physical ability in part because of this damage.

Warning signs of overdose to recognise

Recognising an overdose quickly is often the difference between life and death. Doctors look for three signs together, sometimes called the opioid overdose triad:

1. Pinpoint pupils
2. Slowed breathing
3. Reduced consciousness

In practice, this means looking for a combination of signs. Breathing may be very slow, very shallow, or may have stopped. The person may be making choking or gurgling sounds. Their lips, fingertips, or face may appear blue, purple, or grey, which indicates that oxygen is not reaching the blood. They may be limp and unresponsive, unable to wake even when shaken or called.

In an alcohol overdose, the pupils may be normal rather than pinpoint, but the other signs, including slowed breathing and unresponsiveness, remain the same. If someone shows any of these signs, they need emergency help immediately.

What to do if you or someone else is overdosing

Call 999 and ask for an ambulance. Tell the operator what the person has taken, if you know, and that they are showing signs of overdose. Stay on the line and follow any instructions given.

If the person is unconscious but breathing, place them in the recovery position, on their side with their head tilted back slightly to keep the airway open. This reduces the risk of choking if they vomit. If they stop breathing, the operator may talk you through rescue breaths or CPR.

If naloxone is available and you suspect they have been using heroin or other opioids, administer it. Naloxone temporarily reverses the effects of opioids and can restore breathing within a few minutes. Following a change in UK law in December 2024, pharmacists and other professionals can now supply naloxone without a prescription, and anyone can legally use it to save a life in an emergency.

Stay with the person until help arrives. Naloxone wears off after 20 to 40 minutes, and the overdose may return if the opioid is still in their system. Speak to the 999 operator and ask them what to do next if help still hasn’t arrived.

When an overdose is survived

An overdose is survivable when help arrives quickly. The body’s shutdown is a process, not an instant event, and action before it’s too late can change the outcome. But survival does not always mean full recovery, and the risk of future overdose remains high for anyone who continues to use substances. Research consistently shows that people who survive one overdose are at far higher risk of experiencing another, especially in the first few weeks or months after.

Get help from Bayberry Rehab

For those who have experienced an overdose, or who are using substances in ways that put them at risk, addiction treatment can reduce that risk.

Medically supported detox means withdrawing under medical management to ease symptoms and prevent complications. It removes the immediate physical dependence in a controlled setting.

Rehab therapy and longer-term residential programmes then work on the reasons behind the drug or alcohol use. Bayberry Rehab offers a range of options for people at different stages, with clinical teams experienced in helping people move from crisis toward stability. Contact us today to discuss how we can help you or someone you care about.