Dangers of Energy Drinks Shown by Rise in Caffeine Toxicity Cases

Health professionals in Australia have suggested that revised warning labels be added to energy drinks containing caffeine following a sharp rise in the incidence of caffeine toxicity and overdoses, particularly from teenagers. Callers to the New South Wales Poisons Information Centre reported tremors, heart problems, stomach upsets, dizziness, irregular heart beat, jitters, chest pains and a number of other symptoms after drinking these beverages. Almost 300 calls were made reporting adverse reactions to energy drinks in the 7 years from 2004 - 2010, with more than 30% of these people attending hospital. The results from the study are summarised in the Table below adapted from the paper.

The number of call about caffeinated energy drinks increased five-fold from 12 to 65 from 2004 to 2010. Recreational use of caffeine was the most common reason for the call. The most common symptoms reported included stomach upsets, irregular heart rate, tremors and dizziness. In severe cases caffeine toxicity can resemble amphetamine poisoning,and cause psychosis, seizures, irregular heart beat and very rarely, death.

Energy drinks are very popular especially for young adults and kids
. Source: Public Domain
Caffeine overdoses on the rise
Caffeine overdoses on the rise. Source: Public Domain
Energy drinks are widely advertised
Energy drinks are widely advertised. Source: Public Domain

Teenagers were the most frequent group of callers. The energy drinks were often consumed with alcohol, amphetamines and other stimulants. More than half of the reported cases were male. 'Red Bull' and 'V' represented about 70% of the energy drink-related calls to the centre, followed by 'Mother' and 'Pulse'. No reports of caffeine toxicity caused by coffee or cola drinks occurred during study period. However nearly 550 people reported overdoses from the caffeinated tablets No-Doz and No-Doz Plus. Parents should be aware that many teenagers take these tablets because they cannot stay awake at night to play online games.

A typical can of energy drink can contain up to 300 mg of caffeine. The table shows the caffeine in a range of energy drinks available in Australia. Extra caffeine is added from additives such as guarana. In Australia the caffeine contents shown on the labels includes the total amount of caffeine including that in this and other additives. Guarana, an extract from the plant Paullinia cupana, contains caffeine, theophylline and theobromine in varying quantities. Guarana appears to have no apparent adverse effects other than that linked with the caffeine it contains. The amount of caffeine in guarana (40–80 mg per gram of extract) may not always declared on the packaging. Similarly, taurine, an amino acid added to many energy drinks, is not apparently toxic at the doses used. Ginseng, a herbal extract with claimed for its purported aphrodisiac and mild stimulant properties, has not been reported to be toxic at the dose used.

Caffeine Toxicity

Even a tiny dose of 50 mg of caffeine can induce agitation and rapid heartbeat. Some people may be allergic to caffeine at low dosages. Some manufacturers of energy drinks suggest a maximum of about 200 mg of caffeine per day. This is roughly 1 1/4 500 ml cans of energy drink such as 'Red Bull' or 'V'. The Red Bull website suggests that a person’s intake should be similar to that of coffee. Clearly mean teenagers and older people drink much more than this. The type of symptoms reported to the poison centre was consistent with an overdose of caffeine and stimulant misuse of a serious nature. About 60% of calls for advice came from emergency departments at hospitals. About 25% of the calls reported co-ingestion of alcohol and about 30% of calls reported co-ingestion of caffeine (including tablets) with other stimulants such as amphetamines.

Various studies of American college students have warned of the dangers of the mixing of energy drinks with alcohol, particularly in an attempt to sober up. 

Caffeine Overdose Symptoms

The recommended a safe amount of caffeine is about 300-500 milligrams of caffeine per day. This is of course depends on health, body weight, tolerance through repeated use and individual sensitivity. This is equivalent to about 4 cups of coffee a day or 2-3 energy drinks. Caffeine intake beyond 500 mg per day has been shown in various studies to cause insomnia, nervousness and headaches, but it varies a lot. Caffeine takes some time to work through the body and them is broken down and eliminated. The half-life of caffeine in adults is about 6 hours. This means if you consume 200 mg of caffeine at 6.00am, you would still have 100 mg in your system at noon.

There are a variety of common symptoms that indicate too much caffeine has been consumed. The body can work to metabolise the caffeine in the body and so the dose depends on the rate of ingestion. Consuming massive doses of caffeine all at once is dangerous because there is not enough time for the warning symptoms to develop showing that too much caffeine has been consumed. The common symptoms of potential overdose are:

What is a Caffeine Overdose and can it be Lethal?

It's hard to pinpoint an amount of caffeine that will cause these caffeine overdose symptoms to begin because people have different tolerance levels. Generally a dose between 300-500mg could produce some of the above mild to moderate symptoms, especially in those with no tolerance.

The lethal dose of caffeine in humans varies but is estimated to be about 150 to 200 milligrams per kilogram of body mass. For an average male weighing 80kg this is equivalent to about 1.6 gm and for the average woman weighing 70 kg about 1.4 gm of caffeine. This is roughly equivalent to 80 to 100 cups of coffee (25-200 mg caffeine per cup) for an average adult taken within a limited time frame that is dependent on half-life. This equivalent to about 100 cans of Red Bull (150 mg of caffeine per 500 ml can), for an average adult male, but vomiting would most certainly occur well before that. The lethal dose for No Doz tablets (containing 100mg caffeine) would be about 150 tablets. There have been reported deaths from overdosing on caffeine pills, with serious symptoms of overdose requiring hospitalization occurring for doses of 2 grams of caffeine (2000 mg) in a relatively short period of time.


There is clear evidence of caffeine toxicity caused by over-consumption. The growing number of hospitalisations, particularly in teenagers has suggested that the labels on energy drinks should be improved and regulation imposed controlling caffeine content. The authors of the study recommend that labelling should include National Poisons hotline number and appropriate health warnings. Warning labels similar to those used on as non-prescription caffeine tablets should be used on energy drinks. The labels used for No Doz are shown below.

No Doz Warming (from their website)

No-Doz Plus is a caffeine tablet that contains 100 mg of caffeine plus Vitamin B1 (10mg thiamine hydrochloride) and Vitamin B3 (nicotinic acid) in a base containing glucose. The recommended dosage of No-Doz is one tablet. You should only take one No-Doz tablet in a 3 hour period. Individual responses can vary depending on such factors as age, weight, and tolerance to caffeine. No more than 6 No-Doz tablets should be taken within 24 hours and no more than 5 No-Doz Plus tablets should be taken within 24 hours.


For occasional use only. Not intended for use as a substitute for sleep. If fatigue or drowsiness persists or continues to recur, consult a doctor. The recommended dose of this product contains about as much caffeine as a cup of coffee. Limit the use of caffeine containing medications, foods or beverages while taking this product because too much caffeine may cause nervousness, irritability, sleeplessness and occasionally rapid heart beat. Do not give to children under the age of 12 years of age. As with any drug, if you are pregnant, nursing a baby, have high blood pressure or a heart condition, seek the advice of a health professional before using this product. Keep out of the reach of children. Vitamin supplements should not replace a balanced diet.

Cases of Caffeine Toxiity Reported to NSW Poison Centre

Main ingredients, dose/100 mL
Serving volume (mL)
Total Caffeine per serving
No. of calls
Red Bull
Caffeine, 32mg
Sugars, 11g
Caffeine, 32mg
Guarana extract, 120mg
Ethanol, 7g
Caffeine, 7mg
Caffeine, 32mg
Sugars, 10.5g
Caffeine, 32mg
Guarana extract, 10mg
Ginseng extract, 20mg
Sugars, 13g
Other/ unknown
Cola drinks
Caffeine, approximately 40mg per can (11mg per 100ml)
no cases
Caffeine, approximately 25-200mg per cup
no cases
No-Doz/No-Doz Plus
Caffeine, 100mg / tablet (packs of 24, and 100)