||Unfortunately, as of June 2004, the simple answer is that there have not been any published toxicological studies looking at 2C-I. One assumes that it is similar to 2C-B in its toxicity profile, but that is not a safe assumption, just a common one. 2C-B has not been found to cause the type of serotonin-neuron damage that MDMA does at high doses and it seems to cause smaller increases in heart rate and blood pressure at common recreational doses (10-30mg) than MDMA does at 80-150mg. Although it is likely that 2C-I has similar pharmacology and physical effects based on its similarity of structure and similarity in experiential effects, it is not reasonable to base medical assumptions on the research and data about 2C-B at this time.|
I think the best single-document summary is from the EMCDDA:
As far as combining with MDMA goes, the health issues are likely to be the same as those with MDMA alone at higher doses with an additional increased psychedelic risk profile (increased risk of 'bad trip'-type psychological problems).
So, that means that the guess is that 2C-I+MDMA would pose increased risk of stimulant health issues like racing heart, blood pressure raised for a long period, serotonin syndrome, nausea, vomiting, etc. It is unclear whether there would be an actual, real-world increase in problems because it is possible people would take less MDMA when they combine it with the 2C-I and thus 'balance' the issues a bit. Very hard to say.
And we'd expect a somewhat higher portion of people who use 2C-I instead of just MDMA to have acute anxiety responses, panic attacks, etc. But, again, who knows. We've gotten a few unsubstantiated reports of people seeking medical help from lingering PTSD after higher dose 2C-I experiences, but at this point I wouldn't stress that too much more than just to say that tripping can be very strange and disorienting, and seems clearly to trigger serious mental health problems in a small portion of people who use psychedelics.