Claims by manufacturers include increased energy levels, increased physical endurance, improved physical performance, and better concentration.
But do these claims hold true and are energy drinks safe?
What is in an energy drink?
According to the Australian Drug Foundation , energy drinks usually contain a mixture of:
- Caffeine — the main ingredient in energy drinks, caffeine is a stimulant that acts on the central nervous system to speed up the messages to and from the brain
- Guarana —a plant extract containing around twice the amount of caffeine as coffee beans
- Theobromine — extracted from the cacao plant, this substance is found in chocolate and many other foods, and has a similar effect to caffeine
- Theophylline — structurally similar to caffeine and found naturally in tea at very small levels, this is a drug used for the treatment of respiratory diseases and asthma
- Taurine — necessary for normal skeletal and muscle function, this occurs naturally in food, particularly seafood and meat
- Ginseng — believed to have medicinal properties, this plant-substance has been found to interact with a number of prescription and herbal drugs.
How do energy drinks affect you?
There is no doubt that energy drinks have a real affect — mostly due to the amount of caffeine and sugar in them. Common short-term effects include:
- feeling more alert and active
- stimulated brain and nervous system
- increased heart rate and body temperature
- increase in urination.
However, too much caffeine can have detrimental consequences. According to the Mayo Clinic most adults should not exceed 400mg of caffeine per day. That’s the equivalent of 4 cups of brewed coffee. Excessive consumption (500 to 600mg per day) can lead to:
- sleeping difficulties
- feeling nervous, irritable and restless
- an upset stomach
- experiencing a faster heartbeat
- muscle tremors.
Given that the average 500mL energy drink contains anywhere from 100mg – 160mg of caffeine, it’s easy to see that a few cans per day can easily put you in the ‘excessive caffeine consumption’ category.
Excessive caffeine consumption can also result in serious injury or death. In fact, the Australian Medical Journal reports that cases of caffeine toxicity from energy drink consumption are increasing, particularly among adolescents. 
What does the research say?
- Energy drinks increase blood pressure and heart rate when people consumed two cans per day over the course of a week. These increases were higher at the end of day seven than on day one. 
- Excessive consumption, along with use of alcohol or other caffeinated beverages, may cause adverse reactions such as seizures, disrupted sleep patterns, nervousness, nausea or even death. 
- Using energy drinks as sports drinks before or during exercise may cause restlessness, irritability, rise in blood pressure and higher risk of dehydration. 
- Teenagers who regularly consumed energy drinks may have increased the likelihood of developing mental health problems. Those most likely to consume these drinks also used alcohol, marijuana and were prone to depression. 
- Teenagers who used energy drinks were more likely to illicitly use prescription stimulants. 
Are energy drinks safe?
The Mayo Clinic recommends that the occasional energy drink is fine for most people, although consumers should not exceed the daily limit of 500mL. 
However, some people should avoid these types of beverages. They include:
- children and young people
- pregnant or breastfeeding women
- caffeine sensitive people
You should also avoid combining energy drinks with alcohol.
If you are consuming these beverages because you lack energy, consider looking at your sleep patterns, activity levels and your nutrition. It is far safer to increase energy levels through healthy lifestyle changes, than relying upon drinks that may not be entirely safe. Of course, if your symptoms persist, then see your doctor.
 Australian Drug Foundation, Energy Drinks: do they really give you wings?, October 2012; accessed 7 September 2015 http://www.druginfo.adf.org.au/attachments/810_ADF_Factsheet_energy_web.pdf
 Mayo Clinic, Caffeine: How much is too much?; last updated 14 April, 2014; accessed 7 September 2015 http://www.mayoclinic.org/healthy-living/nutrition-and-healthy-eating/in-depth/caffeine/art-20045678?pg=1
 Naren Gunja and Jared A Brown, Energy drinks: health risks and toxicity, The Medical Journal of Australia, 2012, 196 (1): pp46-49. https://www.mja.com.au/journal/2012/196/1/energy-drinks-health-risks-and-toxicity
 John P Higgins, Troy D Tuttle, Christopher L Higgins, Energy Beverages: Content and Safety, Mayo Clinic Proceedings, Volume 85, Issue 11, pp1033 – 1041, November 2010; accessed 7 September 2015 http://www.mayoclinicproceedings.org/article/S0025-6196(11)60094-3/fulltext#cesec18
 Sunday Azagaba, Donald Langille, Mark Asbridge, An emerging adolescent health risk: Caffeinated energy drink patterns among high school students, Preventative Medicine Journal
Volume 62, March 2014, pp 54-59; accessed 7 September 2015, http://www.sciencedirect.com/science/article/pii/S0091743514000504
 Conrad Woolsey, Laura B Barnes, Bert H Jacobson, Weston S Kensinger, Adam E Barry, Niels C Beck, Andrew G Resnik, Marion W Evans, Frequency of energy drink use predicts illicit prescription stimulant use, Substance Abuse 01/2014; 35(1) pp96-103; accessed 7 September 2015 http://www.researchgate.net/publication/260482627_Frequency_of_energy_drink_use_predicts_illicit_prescription_stimulant_use
 Dr Katherine Zeratsky, Can energy drinks really boost a person’s energy? Mayo Clinic, Last updated 11 February 2015; accessed 7 September 2015 ,http://www.mayoclinic.org/healthy-living/nutrition-and-healthy-eating/expert-answers/energy-drinks/faq-20058349