Recognising the signs of overdose

An overdose happens when a person takes more of a substance than their body can handle. All drugs, and even common substances like salt, sugar and iron tablets, are capable of causing negative health outcomes and even death when taken at high doses. However, overdose happens more with some substances than others.

LD50

LD50, or median lethal dose, is a tool used by scientists to measure the toxicity of substances. LD50 stands for lethal dose 50 – it’s a measurement of the amount of a substance required to kill 50% of the subjects exposed to it. These numbers come from animal models, so they can’t be directly applied to humans, but they give us an idea of the relative lethality of substances. LD50 is usually measured in mg/kg: how many milligrams of a substance are required per kg of body weight to be fatal.

Some drugs have a very high LD-50, making overdose unlikely. It’s possible to overdose on nicotine – but the dose required is so high that this is very rare. Similarly, it is possible to overdose on LSD, but the amount needed is many, many times higher than the recreational dose, which is thought to be about 50-200 micrograms. A 2020 paper records a case study of a woman who survived the accidental ingestion of 55mg of LSD – 550 times the recreational dose.

Overdose is most likely when the LD50 of a substance is very close to the recreational dose. The LD50 of alcohol is thought to be a blood alcohol level of 0.4%. You would need to drink heavily to reach this level of alcohol intoxication, but it can happen accidentally. Drinking on an empty stomach, having a lower body weight and drinking very quickly all accelerate blood alcohol concentration and increase the risk of overdosing.

Some substances have wafer-thin margins between a recreational dose and an overdose, and this makes them particularly dangerous. Just 3mg of fentanyl can kill an adult male. Because the lethal dose is so small, and it’s not possible to tell how much of a substance you’re getting when buying on the street, the risk of overdose is extremely high.

One of the symptoms of drug addiction and alcohol addiction is increased tolerance, which complicates things further. Someone with a high tolerance will be able to take more of a drug than someone who has never taken it, so it isn’t possible to definitively say how much of a substance will cause an overdose. This can also have dangerous consequences for people who relapse from addiction treatment or drop out of rehab – they may take a dose of a drug that their body could handle when they were using regularly but not be able to tolerate it.

Common substances that can cause overdoses

Opioids, stimulants and benzodiazepines are the drugs most commonly seen on death certificates in the case of overdose in the UK. It’s easier to overdose on opioids than alcohol, but alcohol overdoses were about five times higher in 2022, killing about 10,000 people. This is because alcohol is consumed by many more people than opioids.

Overdose symptoms vary depending on the substance taken – but there are some general overdose symptoms to look out for. If you spot any of these symptoms, call 999 immediately. Do not attempt to sober up the person yourself, like forcing someone to drink coffee if they’re overdosing on alcohol – this can waste valuable time. The exception to this is opiate overdoses if you have access to naloxone, which you should administer immediately if someone is overdosing. General signs of overdose include:

• Unresponsiveness and unconsciousness
• Difficulty breathing or irregular breathing
• Significantly altered heart rate – either very high or very low
• Chest pain
• Seizures
• Vomiting
• Confusion, agitation and hallucination.

Common overdose symptoms by substance

Opioids – Paleness, clamminess, blue or purple lips or fingernails, vomiting or gurgling noises, unconsciousness, slowed or no heartbeat.

Stimulants – Overheating, flushing, chest pain, rigid muscles, seizures, difficulty breathing, agitation, high heart rate, heart attack.

Alcohol – Vomiting, seizures, slow heart rate, clamminess, low body temperature, low heart rate, unconsciousness.

Benzodiazepines – slurred speech, slow heart rate, unconsciousness.

Benzodiazepine overdose on its own is rare – it usually becomes fatal if benzos are mixed with other downers, like opioids or alcohol.

Overdose symptoms have a lot of crossover between substances, particularly between stimulants and downers. Keep an eye on your friends, and try to be aware of what they’re taking – this can be lifesaving, especially if they’re overdosing on opioids and you have access to naloxone.

Long-term impact of an overdose

There can be extremely severe consequences if you survive an overdose. If you stop breathing or your heart stops as a result of acute intoxication, your brain can be damaged. This is because brain cells start to die very quickly without oxygen – within about five minutes. This can cause a variety of outcomes, ranging from moderate to severe – speech, movement, and judgement can be impaired, but in extreme circumstances, this can lead to a persistent vegetative state. The likelihood of recovery depends on how long the brain was starved of oxygen – so it’s important to know the signs of overdose and do everything you can to prevent it.

Overdose prevention

Preventing overdose means practising harm reduction. It isn’t possible to eliminate risk, but there are things you can do to reduce it.

• Test your drugs

The risk increases significantly if you don’t know what you’re taking. Many drugs are mis-sold as other substances or contaminated with other substances. ‘Street benzos’ are often mis-sold as popular benzos like diazepam – so you could think you’re getting diazepam but end up with another benzo like temazepam or etizolam. These drugs can interact with your system differently and may be stronger or last longer. Your drugs could also be contaminated with other dangerous compounds like nitazenes – or be an entirely different substance that you weren’t expecting.

• Educate yourself

Learn the symptoms of overdose and what to look for, and educate others to be aware of them, too.

• Don’t use alone

Having someone with you can save your life. Do not use drugs when you’re on your own – you could need someone to get urgent medical assistance for you.

Get help

Overdoses claim thousands of lives every year – and drug use is never risk-free. One of the most common addiction symptoms is prioritising drug or alcohol use over your health – and this puts you at risk of overdose.

Addiction recovery is not easy – but we can help. Our addiction rehab services can help you get on the path to a healthier, happier life.