Where else can one go, from 2C-I? The iodine is the fourth, and the last of the so-called halogens, at the bottom of the classical periodic table. But, thanks to the miracles that have accompanied us into the nuclear age, there is a fifth halide now known, Astatine. All of its isotopes are radioactive, however, and it seems unlikely that there will ever be an entry (other than this one) for 2,5-dimethoxy-4-astatophenethylamine. What might be speculated as to its activity? Probably similar in potency to 2C-I, requiring maybe 10 or 20 milligrams. The duration would be dicey to measure, since the isotope with the longest known half-life is half decayed in about 8 hours, and the longest lived natural isotope (for those who insist on natural rather than man-made things) is half decayed in less than a minute. Two predictions would be pretty solid. You might have quite a job accumulating your 10 milligrams of Astatine, as the most that has so far been made at one time is only about 0.05 micrograms, approximately a millionth of the amount needed. And the second prediction? You would not survive the screaming radiation that would bombard you if you could get the needed 5 or 10 milligrams of radio-astatine onto that magic 4-position, and the resulting 2C-A into your tummy!