(covers information from several alternate timelines)
Acute radiation syndrome, colloquially known as radiation poisoning, radiation sickness, or localized as radiation burns, was a form of organic tissue damage caused by exposure to ionizing radiation. Symptoms varied with the severity of exposure but often included fatigue, nausea, vomiting, and hair loss. Radiation could cause sterility and cancer, and, given a large enough dose, could be lethal.
Radiation effects could be countered for a short time with hyronalin, though adrenaline was once a treatment as well. Extreme cases of theta radiation poisoning could be treated with arithrazine. (VOY: "The Omega Directive") By the 24th century, cellular damage by radiation could be prevented by taking special inoculations. Radiation poisoning could also lower calcium levels. (DS9: "Visionary") Exposure to delta radiation also caused severe disfigurement, which could be considered a form of radiation poisoning as well. (ENT: "In a Mirror, Darkly"; TOS: "The Menagerie, Part I") The only know cure for radiation poisoning was Nanoprobes. (VOY: "Friendship One")
In 2056, Colonel Phillip Green ordered the euthanasia of millions of Humans afflicted with radiation poisoning from World War III in order to prevent their damaged genes from being passed on to future generations. (ENT: "Demons")
In 2063, Lily Sloane was affected by theta radiation poisoning. It came from the Phoenix's throttle assembly, which was damaged by the Borg's attack on Bozeman, Montana. Dr. Beverly Crusher later treated her condition on the USS Enterprise-E. (Star Trek: First Contact)
In 2266, while on an inspection tour of an old class J training vessel, Fleet Captain Christopher Pike was caught in a delta radiation leak resulting from a baffle plate rupturing. He managed to evacuate most of the cadets, but the lockdown trapped him in the irradiated engine room, resulting in severe radiation burns that hopelessly crippled him. (TOS: "The Menagerie, Part I", DIS: "Through the Valley of Shadows")
In 2285, after repairing the USS Enterprise's warp drive and allowing it to escape Khan Noonien Singh's detonation of the Genesis Device, Captain Spock was affected by radiation poisoning and eventually died from it. (Star Trek II: The Wrath of Khan)
In 2259 of the alternate reality, Kirk and Spock's positions were reversed during their confrontation with Khan: Kirk poisoned himself repairing the USS Enterprise's warp core before the ship crashed to Earth. Fortunately, Spock apprehended Khan and Leonard McCoy performed a blood transfusion to revive Kirk. (Star Trek Into Darkness)
As a result of depletion of their ozone layer, the Aldeans suffered from radiation poisoning. One of the results was infertility. Doctor Beverly Crusher discovered this problem. (TNG: "When The Bough Breaks")
In 2370, the debris from a crash-landed Federation probe caused radiation poisoning within the Barkonians on Barkon IV. Lieutenant Commander Data was able to get a cure and administered it into the community well. (TNG: "Thine Own Self")
Between 2248 and 2378 the probe Friendship 1 crashed on Otrin's homeworld and the citizens accidentally used it's antimatter warp drive to power their electrical grid. As a result because of damage to the probe and the citizens inexperience with antimatter; a containment failure caused a warp core breach and the core went critical releasing toxic Antimatter radiation into their atmosphere and gave them radiation poisoning. The crew of USS Voyager used Seven of Nine's nanoprobes plus modified photon torpedoes to treat their radiation poisoning and save their world. (VOY: "Friendship One"