http://www.ncbi.nlm.nih.gov/pubmed/16889759
Although caffeine alone failed to alter body temperature, it potentiated MDMA-induced hyperthermia. This association also significantly increased MDMA lethality (from 22% to 34%). Following administration of MDMA to rats, there was a persistent decrease in the number of serotonin transporter sites in the cortex, striatum and hippocampus, which was potentiated by caffeine co-treatment. This MDMA toxicity in rats was accompanied by a transient dopaminergic impairment in the striatum, measured as decreased [(3)H]WIN35428 binding sites, by 31% 3 days after treatment, which was not modified by caffeine. A transient down-regulation of 5-HT(2) receptors occurred in the cortex of MDMA-treated rats, whose recovery was slowed by co-treatment with caffeine
http://www.wired.com/wiredscience/2008/02/caffeine-and-ec/
To test their theory, the scientists injected the drugs into Sprague Dawley rats and then probed them with a rectal thermometer. When the unlucky critters received both chemicals, their body temperatures increased far more than when they were given MDMA or caffeine alone.
Harkin and his team followed up with some very thorough work in an attempt to understand how the two chemicals interact. By giving rats a combination of caffeine and other drugs that have well-known effects on the brain, they were able to conclude that dopamine receptors, a type of nerve signaling protein, play a big role in the unusual overheating.
http://www.ncbi.nlm.nih.gov/pubmed/22671762
Co-administration of caffeine profoundly enhances the acute toxicity of MDMA in rats, as manifested by high core body temperature, tachycardia and increased mortality. In addition, co-administration of caffeine enhances the long-term serotonergic neurotoxicity induced by MDMA. Observations to date support an interactive model of drug-induced toxicity comprising MDMA-related enhancement of dopamine release coupled to a caffeine-mediated antagonism of adenosine receptors in addition to inhibition of PDE
http://www.sciencedirect.com/science/article/pii/S0014299906012490
Caffeine promotes hyperthermia and lethality when co-administered with the recreational drug 3,4-methylenedioxymethamphetamine (MDMA, “Ecstasy”) to rats. In the present study, co-administration of caffeine (10 mg/kg, s.c.) with MDMA (10 mg/kg, s.c.) induced a profound tachycardic response compared to rats treated with either drug alone. However, neither caffeine (30 μM) nor MDMA (1–30 μM), alone or in combination, affected the electrocardiogram of the isolated heart suggesting that central and sympathomimetic actions, rather than direct actions of these drugs on the heart, are responsible for the tachycardia observed in vivo. This is a serious drug interaction, which could have important health consequences for recreational drug users.
This is just a quick search, but i have read more about it in the past.. Including a slight potentiation when caffeine is taken prior to MDMA wich resulted in longer duration and increase of effects(and side effects)..
My guess would be to take the 5 hour energy in advance and take extra care to stay cool and hydrated.. Taking high dose caffeine pills seems like a bad idea to me now, i have done this in the past and have to admit i felt shittier after, even though i do believe it enhanced the overall experience.
My 2 cents
PS. I have not found any evidence of a human death resulting from co-administration of caffeine, but the fact that it does increase these dangers, will hopefully make you consider ditching the caffeine or atleast lower the dose.
Stay safe