Lissberry Poisoning

Lissberry poisoning is caused by the ingestion of a shrub-growing berry of dark purple-blue coloration. The symptoms caused are often quite severe, but only lethal in a fraction of cases. The condition is known for being unpredictable as the severity of symptoms vary a lot from patient to patient and are often not easily predictable from the quantity consumed.
Symptoms include vomiting, diarrhea, convulsions, dizziness, breathing difficulties and arrhythmia. Onset is fairly rapid, with initial symptoms within an hour of consumption. When lethal, the cause of death is commonly heart failure or respiratory failure, though in many cases the precise cause of death is not clear. There appears to be a critical window of about six to ten hours from ingestion, during which symptoms are much more likely to be lethal. Once this initial time has passed, the risk of death drops nearly to zero. 
When not lethal, symptoms usually persist over a number of days and gradually subside. It is not uncommon for milder symptoms such as fatigue, weakened lungs, light arrhythmia and stomach troubles to continue for weeks or months or even, in rare cases, become chronic. 
Lissberry is quite prevalent in its native region. Due to its visual similarities with some local varieties of edible plants, accidental ingestion is relatively common particularly among children. 
In recent years, apothecaries have been able to create an antidote which reliable counteracts the worst effects of the poison if administered within the first hours of consumption. After the critical treatment window has passed, it will generally do little beyond shortening the recovery time by a day or two. As the side-effects of the antidote can themselves be fairly severe, though not deadly, treatment is not usually administered if the patient has stabilized and the dose does not appear likely to be lethal.