TLDR: All the ingredients have approval to be in the drink and have had toxicity testing done. However the scope of this testing is considered to be limited in certain cases and there may be a risk at the quantities included in certain energy drinks.
According to the Red Bull website:
Red Bull contains taurine, glucuronolactone, caffeine, B vitamins, sucrose, and glucose.
Red Bull sugar-free also contains aspartame, acesulfame K, and sucralose in place of sucrose and glucose.
This study Opinion on Caffeine, Taurine and D-Glucurono - g -Lactone as constituents of so-called "energy" drinks (expressed on 21 January 1999) published by the EU looked specifically at "the safety of caffeine, taurine and D-glucurono- g -lactone as constituents of so-called "energy" drinks."
And found the following:
It concluded at that time that there
was no apparent reason for concern
about carcinogenic or mutagenic
effects of caffeine in man at normal
levels of intake.
Toxicological studies did not reveal
any indication for a genotoxic,
carcinogenic or teratogenic potential
of taurine. 52-64 However, there is no
adequate study on chronic
Investigation of subacute/subchronic
toxicity has also been fragmentary.
65-71 Overall, the available data are
insufficient to establish an upper
safe level for daily intake of
The available toxicity studies are
extremely limited. Acute toxicity
studies have been carried out in rat,
mouse, dog, rabbit and cat by oral,
intravenous, intraperitoneal and
subcutaneous routes. 76 It is of low
acute toxicity, with the oral route
being the least toxic;
Human metabolic considerations
indicate the body is likely to handle
small quantities of glucuronolactone
without any problems. However, the
intake of glucuronolactone from
consumption of some "energy" drinks is
possibly as much as two orders of
magnitude greater than that from the
rest of the diet. There is very little
information available for risk
assessment of glucuronolactone at such
intakes. While there is no indication
from the available data that there is
any risk to health from consumption of
high amounts of glucuronolactone,
there is a lack of scientific evidence
to support the safety of
glucuronolactone present in beverages
at concentrations that may result in
intakes as much as two orders of
magnitude greater than that obtained
from the rest of the diet. As was the
case with taurine, there is
insufficient information on which to
set an upper safe level for daily
intake of glucuronolactone.
Taken from Borror0's answer to this question Does aspartame cause cancer?:
According to the National Health Institute, there is no evidence suggesting aspartame causes cancer:
A study of about half a million people, published in 2006, compared people who drank aspartame-containing beverages with those who did not. Results of the study showed that increasing levels of consumption were not associated with any risk of lymphomas, leukemias, or brain cancers in men or women. (Question 2)
Researchers examined the relationship between aspartame intake and 1,888 lymphomas or leukemias and 315 malignant brain cancers among the participants of the NIH-AARP Diet and Health Study from 1995 until 2000. Development of these cancers was not associated with estimated aspartame consumption, refuting a recent animal study with positive findings for lymphomas and leukemias and also contradicting claims regarding brain cancer risk. (Questions 3 and 8)
Acesulfame potassium (also known as
ACK, Sweet One®, and Sunett®) was
approved by the FDA in 1988 for use in
specific food and beverage categories,
and was later approved as a general
purpose sweetener (except in meat and
poultry) in 2002.
Before approving these sweeteners, the
FDA reviewed more than 100 safety
studies that were conducted on each
sweetener, including studies to assess
cancer risk. The results of these
studies showed no evidence that these
sweeteners cause cancer or pose any
other threat to human health.
However there are several journals etc. that say testing on artificial Acesulfame K was conducted in the past, was limited in scope and more modern equipment and testing methods area available and more adequate long-term carcinogenicity testing should be conducted.