Lesser-Known Overdose Effects
Friday, 15 May, 2026
When people talk about overdose, the conversation usually goes to one place: respiratory depression. That's the medical way of saying your breathing slows down or stops. It's real, it's deadly, and it's why NUAA pushes so hard to get naloxone into people's hands. But breathing isn't the only thing at risk.
Your body goes through a lot when you overdose, especially if you're unconscious for any amount of time. Some of these effects don't show up for hours or even days. Some people get out of hospital fine, then find out weeks later that their kidneys are in trouble, or that they've got a serious lung infection. There have also been rare cases where people have lost their limbs.
Understanding these uncommon overdose risks means you can look after yourself and the people around you. Here’s what you need to know.
Compartment Syndrome: Lost Limbs
Research has identified this as a real danger for people who overdose and lose consciousness, and the consequences can be permanent.
Here's what happens: when you lose consciousness, you don't move. You might collapse in an awkward position, with an arm underneath you, a leg bent against the floor, or your weight pressing down on one part of your body for hours. That constant pressure cuts off blood flow to the muscles in that area.
Your muscles are wrapped in tight bands of tissue called compartments. When blood flow gets cut off and then suddenly returns, those muscles swell up. But the compartments can't stretch to fit the swelling, so the pressure inside builds up.
This is called Acute Extremity Compartment Syndrome, or "compartment syndrome" for short, and it's considered a medical emergency.
Without urgent treatment, compartment syndrome can permanently destroy muscle and nerve tissue. In severe cases, surgeons have to cut open the skin to relieve the pressure, a procedure called a fasciotomy. In the worst cases, amputation becomes necessary to save someone's life. Once the pressure inside a compartment rises high enough, doctors need to operate within hours.
Warning signs:
These can appear hours after the overdose, don't dismiss them as just 'soreness' from sleeping awkwardly.
Severe pain in an arm, hand, leg or foot
The limb feels very tight or 'full,' almost hard to the touch
Numbness, tingling, or 'pins and needles' that won't go away
Weakness, trouble gripping, moving fingers or toes
Skin that looks pale, shiny, or a strange colour
If you notice any of these after an overdose, yours or someone else's, go to emergency immediately or call 000. Tell them you think it might be compartment syndrome from falling unconscious. Time matters.
Compartment syndrome from overdose is different from the more common sports injury version because the muscles affected tend to be different, and it's harder for doctors to know exactly how long the injury has been going on. This means it can be missed or diagnosed late. Being your own advocate, or someone else's, is really important here.
A big part of preventing compartment syndrome is not using alone, and making sure someone who overdoses is placed in the recovery position on their side, so their limbs aren't compressed under their body weight for extended periods.
Rhabdomyolysis: Dissolving Muscles
Rhabdomyolysis, or "rhabdo", sounds technical, but here's the plain version: your muscle cells break down and release their contents into your bloodstream. This can damage your kidneys, mess with your heart rhythm, and make you seriously ill.
Rhabdomyolysis can be triggered by illegal drugs, alcohol, medications, and injuries. In overdose situations, it happens because:
Your muscles are compressed or crushed while you're unconscious (links directly to compartment syndrome)
Some drugs like cocaine and methamphetamine directly damage muscle tissue by compromising function of the heart
Overheating (hyperthermia) during a stimulant overdose, including MDMA, severely overworks muscles
Prolonged seizures exhaust and tear muscles
Ten to 50% of people who develop rhabdomyolysis go on to have acute kidney injury, sometimes needing dialysis. Early treatment makes a huge difference to outcomes.
The most alarming symptom is dark, brown, or cola-coloured urine. This is caused by a muscle protein called myoglobin flooding your kidneys. It looks like tea or Coca-Cola and it is not normal.
Other signs include muscle pain, swelling, and weakness, especially in areas that were compressed during the overdose.
If you notice this symptom after an overdose, go to your nearest emergency department. There they will treat by using IV fluids to flush the kidneys, monitoring for kidney function, and sometimes dialysis if the kidneys are badly affected.
The good news: if caught early, most people fully recover kidney function.
Hyperthermia: Cooking from the Inside
Stimulant drugs including speed, ice (methamphetamine), cocaine, and MDMA can cause your body temperature to spike. This is called hyperthermia. It’s a genuine medical emergency that can cause multi-organ failure if untreated.
Unlike a regular fever, drug-induced hyperthermia doesn't respond to paracetamol or ibuprofen. The brain's temperature control system is disrupted by the drugs themselves, so normal anti-fever medicines don't work. Cooling the body physically with ice packs, fans, or cooling blankets is required, usually in hospital.
What makes hyperthermia especially dangerous is that it triggers a chain reaction. Extreme body heat accelerates muscle breakdown (rhabdomyolysis), which then damages the kidneys. It can trigger blood clotting problems. In severe cases, it can cause multi-organ failure.
Warning signs:
Skin that feels burning hot to the touch
Confusion, agitation, or bizarre behaviour after stimulant use
Muscle stiffness or rigidity
Rapid heart rate with very high temperature
Collapsing or loss of consciousness after taking stimulants
Harm reduction tips for stimulant use:
Stay hydrated but don't over-drink plain water. Sports drinks or water with electrolytes are better if you're active.
Take breaks from dancing or physical activity to cool down. Hot, crowded environments increase the risk of overheating.
Avoid mixing stimulants with other substances that also raise body temperature.
If someone seems extremely hot, confused, or stops sweating while obviously still affected seek medical attention.
Aspiration Pneumonia: Vomit in your Lungs
This is probably the most common 'hidden' overdose complication, and it explains why people sometimes end up in ICU after an overdose even when they seem to have woken up fine.
When you lose consciousness, your body loses the protective reflexes that normally keep food and vomit out of your lungs. If you vomit while unconscious, which is common with opioids, alcohol, and many other substances, stomach contents can flow down into your lungs instead of out of your mouth.
There are two things that can go wrong:
Chemical pneumonitis: the acid from your stomach burns your lung tissue. Symptoms come on fast, within minutes to hours, and include sudden breathlessness and cough.
Aspiration pneumonia: bacteria from your mouth or stomach infect your lungs. This takes longer, often one to three days, and causes fever, cough, chest pain, and difficulty breathing.
Around 10% of people admitted to hospital after a drug overdose develop aspiration pneumonitis. That's one in ten.
Many people don't realise they've aspirated until days later when they start feeling ill. If you had an overdose and then developed a cough, fever, or chest pain over the following days, see a doctor. Tell them about the overdose.
The best way to prevent this? The recovery position. Putting someone on their side with their head tilted means vomit drains out of the mouth, not into the lungs. This single action saves lives and prevents serious lung injury.
The Recovery Position
If someone has overdosed and is breathing but unconscious, put them in the recovery position immediately:
Kneel beside them and place their nearest arm out at a right angle to their body.
Bring their far arm across their chest and hold the back of their hand against their nearest cheek.
With your other hand, pull up their far knee so the foot is flat on the ground.
Roll them toward you, resting their cheek on their hand. Make sure the airway is clear.
Tilt their head back slightly to keep the airway open.
Stay with them. Call 000. Give naloxone if available for opioid overdose.
The recovery position also reduces the risk of compartment syndrome by preventing the body from pressing on one limb for extended periods.
Brain Injury from Overdose
Most people know overdose can kill you. What fewer people know is that a non-fatal overdose can permanently damage your brain.
According to Synapse Australia, areas of the brain most vulnerable to oxygen deprivation include those responsible for memory, movement, and coordination. Brain cells can start dying within minutes of being starved of oxygen.
There are two types of injury depending on severity:
Hypoxic brain injury: reduced oxygen reaches the brain; breathing is happening but not well enough.
Anoxic brain injury: oxygen to the brain stops completely, such as during cardiac arrest or full respiratory failure.
The effects range widely. Some people recover fully. Others are left with long-term impairments in memory, attention, speech, movement, and balance. Research estimates that for every overdose death, there may be 20–30 non-fatal overdoses, and that many survivors are living with undiagnosed brain injuries.
The problem is that brain injury from overdose is often missed. The person wakes up, naloxone is given, and everyone breathes a sigh of relief. But the cognitive effects might not be noticed until later on.
Warning signs:
Memory problems, such as forgetting recent events, or confusion about time
Difficulty concentrating or following conversations
Changes in personality, mood or behaviour
Problems with balance, coordination or walking
Slurred speech or difficulty finding words
Fatigue that doesn't improve with rest
If you or someone you know has these symptoms after an overdose, ask your GP or health worker for a cognitive assessment. Tell them about the overdose. You may be eligible for support services through the National Disability Insurance Scheme (NDIS) if brain injury affects day-to-day functioning.
Synapse, Australia's brain injury support organisation, has information and support services specifically for acquired brain injury. Visit synapse.org.au or call 1800 673 074.
Delayed Post-Hypoxic Leukoencephalopathy: Delayed Brain Danger
This one is rare, but alarming enough that it deserves a mention. It's called Delayed Post-Hypoxic Leukoencephalopathy, DPHL for short. It's a condition where someone appears to fully recover from an overdose, only to become seriously ill again weeks later.
Here's how it works:. Aan opioid overdose damages the brain's white matter, or the tissue that connects different brain regions. After the overdose, the person recovers and seems fine, this is called the 'lucid interval.' Then, one to four weeks later, neurological symptoms return without warning.
If this happens, it's not a new overdose. It's a delayed reaction to the first one.
Research describes patients presenting with confusion, loss of motivation, inability to speak, and loss of bladder and bowel control.
The symptoms can include confusion and disorientation, agitation or aggression, Parkinson's-like tremors, inability to speak or move, and in some cases a state called akinetic mutism, where the person is awake but completely unresponsive.
The good news is many cases do eventually recover, but recovery can take months and may require intensive rehabilitation. Rare cases may result in permanent disability.
If someone who had an overdose weeks ago suddenly becomes confused, stops speaking normally, develops movement problems, or becomes unresponsive, this is a medical emergency. Call 000. Tell emergency services about the prior overdose and mention the possibility of delayed post-hypoxic leukoencephalopathy.
Do not assume this is just intoxication. The person may not have used any drugs at all.
Opioid-Associated Amnesia: Sudden Memory Loss
This is one of the most disturbing and least-known consequences of high-potency opioid overdose, particularly fentanyl. People have woken up from overdoses with no memory of who they are, where they are, or what has happened to their life.
The condition is called Opioid-Associated Amnestic Syndrome (OAS). A landmark case series first identified in Massachusetts found patients presenting with sudden, severe amnesia, and distinctive damage visible on brain MRI scans showing injury to the hippocampus, the brain's primary memory centre.
The hippocampus is especially vulnerable to oxygen deprivation. Research explains that fentanyl can also directly damage hippocampal neurons, causing cells to fire out of control, on top of the hypoxic (oxygen deprivation) injury from respiratory depression. This double hit may explain why fentanyl seems particularly linked to this condition.
Warning signs:
Waking up not knowing who they are or where they are
Unable to recall personal history, family, or recent events
Confusion that doesn't resolve with time or reassurance
Memory impairment lasting more than 24 hours after the overdose
This condition is still rare and not fully understood, but awareness is increasing as fentanyl becomes more prevalent in the Australian drug supply.
If someone wakes from an overdose with significant memory loss, they need urgent neurological assessment, not just a standard overdose discharge.
Sudden Hearing Loss & Vision Problems
This one surprises most people. A 20-year review of cases from a major US poison centre identified 41 people who experienced full or partial hearing loss following opioid exposure, more than half had used heroin. Twelve people became completely deaf.
The inner ear is highly sensitive to both oxygen deprivation and to the direct toxic effects of opioids. In some experimental studies, it is show that the cochlea, the snail-shaped organ that processes sound, contains opioid receptors.
A medical case study found that heroin overdose can cause sudden, severe bilateral hearing loss, affecting both ears, often accompanied by tinnitus (ringing) and balance problems.
The good news is that in most documented cases, hearing loss linked to opioid overdose is reversible, usually improving over days to weeks with appropriate treatment.
However, around 21% of affected patients showed no improvement before hospital discharge, and some cases do result in permanent hearing impairment.
The risk appears highest when heroin is combined with alcohol, particularly in people who have returned to using after a period of abstinence. Visual disturbances have also been reported in cases of combined opioid and cocaine overdose.
After an overdose, tell your doctor if you notice:
Muffled hearing, or ringing or buzzing in the ears
Difficulty hearing voices or sounds that were clear before
Feeling off-balance or dizzy
Blurred vision or unusual visual changes
Early treatment with steroids and other medications may improve the outcome, but only if the connection to the overdose is identified. Be honest with your trusted medical professional about what happened.
Paradoxical Reactions: When Drugs do the Opposite of What They’re Meant To
Drugs don't always do what they're supposed to. Sometimes a drug that normally makes you calm makes you agitated. Sometimes a stimulant makes you fall asleep.
These are called paradoxical reactions, and they can be dangerous because bystanders and even medical staff may misread what's happening.
Common paradoxical reactions:
Benzodiazepines causing agitation: Drugs like diazepam (Valium) are meant to calm. In some people, particularly those with a history of alcohol use, or the very young or elderly, they can instead cause intense agitation, aggression, confusion, or disinhibition. This is called a paradoxical benzodiazepine reaction and affects less than one percent of users, but it's frightening when it occurs.
Opioids causing seizures: Opioids can lower the seizure threshold, particularly certain opioids in high doses. This is partly due to excitation of the brain. Seizure activity in an overdose context is extremely dangerous and requires immediate medical attention.
Stimulants causing sedation: In some people, stimulants like amphetamines can cause drowsiness or calming instead of the expected alertness. Although, this can be a ‘normal’ reaction for people with ADHD.
Naloxone causing severe agitation: While naloxone saves lives, it can cause sudden, severe opioid withdrawal, causing extreme agitation, combativeness, and distress. This is not a new overdose, but it can look like one.
If someone you're with becomes agitated, confused or has a seizure after taking drugs, even a drug that 'should' cause sedation, don't assume it's not serious. Call 000. Unexplained agitation, especially when mixed with signs of overdose, needs medical assessment.
If you've given someone naloxone and they become very distressed and agitated, this may be opioid withdrawal. Stay calm, keep them safe, and call 000 if you're concerned.
Permanent Organ Damage: The Long Game
Some people survive an overdose only to find weeks, months, or years later, that their liver or kidneys are failing. Overdose doesn't just create a crisis in the moment. It can leave behind permanent damage that shortens lives.
Liver damage:
Paracetamol overdose is the most common cause of acute liver failure in Australia. When paracetamol is taken in large doses, including by people trying to harm themselves or people who take it with alcohol, it can cause catastrophic and sometimes irreversible liver damage. The liver injury doesn't peak immediately, it develops over 24–72 hours.
Liver failure from paracetamol overdose remains one of the leading causes of liver transplant in this country. Other drugs including alcohol, cocaine, and MDMA can also cause acute liver damage, either directly or through hyperthermia and rhabdomyolysis.
Kidney damage:
As covered in the rhabdomyolysis section, kidney damage from muscle breakdown is a real risk after overdose. But the kidneys can also be damaged directly by low blood pressure during an overdose, by the direct toxic effects of some drugs, and by repeated overdoses over time. Early treatment dramatically improves kidney outcomes, but left untreated, the damage can be permanent, requiring dialysis or transplant.
Heart damage:
Stimulant overdoses, particularly cocaine and methamphetamine, can cause heart attacks, cardiac arrhythmias, and cardiomyopathy (weakening of the heart muscle). These effects can occur even in young, otherwise healthy people. Some cardiac damage from stimulant use is cumulative and permanent.
If you use drugs regularly, ask your GP or trusted health worker about kidney and liver function tests. These are simple blood tests. Catching damage early means treatment can start before things become serious.
You shouldn't need to explain or justify your drug use to get basic blood tests. If a health worker is making you feel judged, you can call the NUAA PeerLine on 1800 644 413 for support navigating the health system.
Staying Safer
A lot of these complications are connected. Compartment syndrome can cause rhabdomyolysis. Rhabdomyolysis can cause kidney failure. Hyperthermia triggers rhabdomyolysis. Unconsciousness from any cause, including being brought back with naloxone, can have caused aspiration you don't know about yet.
Ways to reduce risks
Don't use alone: Have someone you trust with you just in case
Recovery position, every time: It prevents aspiration, reduces limb compression, and helps clear the airway
Get naloxone and know how to use it: it's available through NUAA, or at many pharmacies and NSPs across Australia
After an overdose, go to hospital even if you feel okay: Brain injury, lung damage, and kidney injury are often invisible for hours
Tell hospital staff about the overdose: they need to know what drugs were involved and how long you were unconscious. Be honest.
Watch for warning signs in the days AND weeks after: dark urine, limb pain, chest symptoms, fever, confusion, memory problems, hearing changes
Watch for delayed brain symptoms 1–4 weeks later: confusion or neurological changes after seeming 'fine' is a medical emergency
Get regular blood tests: kidney and liver function checks are simple and can catch damage before it becomes permanent
An overdose is not just a moment that passes. It can leave marks on your brain, your kidneys, your lungs, your heart, and your hearing. Sometimes immediately, sometimes weeks later. Reducing risks, knowing what to look out for, and getting checked out if you do overdose is how you protect your future self.