This claim is true, Redbull as well as other energy drinks have a wide variety of negative effects on human health. The National Library of Medicine confirms this claim with a large extent of research on the topic. The NLMs analysis "shows a significant prevalence of adverse effects, particularly on the cardiovascular and neurovegetative systems." Redbull, like most energy drinks contains large amounts of caffeine, added sugars, other additives, and legal stimulants such as guarana, taurine, and L-carnitine, These legal stimulants can increase alertness, attention, and energy, as well as increasing blood pressure, heart rate, and breathing. Consumption of energy drinks like Redbull has recently been leading to a wide range of adverse health affects on adolescents ranging from mental affects like anxiety and nervousness to more severe physical outcomes like rhabdomyolysis or acute kidney injury and in some cases even death. This wide range of health issues linked with the consumption of energy drinks confirm the truth behind the claim that Redbull is unhealthy physically and mentally.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10535526/#abstract1
An additional article done by the Cleveland Clinic confirms the research done by the NLM and the above claim. The Cleveland Clinic offers the fact that coffee, another stimulant does not have the same negative effects as that of energy drinks. They say that though excessive amounts of caffeine can be harmful, you would need to consume multiple cups of coffee per day for coffee to really be considered unsafe. Energy drinks on the other hand have oftentimes significantly more caffeine in them as well as other additives like taurine, an amino acid that alone may have some health benefits, but really shouldn't be combined with excessive amounts of caffeine. The Cleveland Clinic concludes that though energy drinks like Redbull are not neccesarily good for human consumption, the "occasional consumption of energy drinks by healthy people is not likely to be harmful, but drinking them regularly can increase your risk of adverse health effects, especially if you have an existing medical condition."
https://health.clevelandclinic.org/are-energy-drinks-bad-for-you
Overall, this claim is true, Redbull is not healthy for human consumption and it can have adverse physical and mental affects on people who consume it regularly.