You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

If you don't know where you are going, you can't tell if you have arrived: defining goals for drug safety announcements. One of the responses available to drug regulators facing a potential drug safety issue is to release a "Dear Doctor" letter describing the problem. Although numerous such safety alerts are issued every year, we know almost nothing about their effectiveness in improving patient outcomes. The article by Reber et al. in this issue is important because it is one of the few studies to examine the effect of such safety alerts on physician behavior.
{"Chemical": []}