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:

Cigarette craving and withdrawal symptoms during temporary abstinence and the effect of nicotine gum. RATIONALE: It is widely believed that nicotine withdrawal symptoms appear within a few hours of stopping smoking, but few data exist documenting their emergence in naturalistic settings. In several countries, nicotine replacement products are licensed for relief of withdrawal symptoms during temporary abstinence, but again, there are no data supporting this from naturalistic settings. OBJECTIVES: To examine the emergence of cigarette craving and withdrawal symptoms during temporary abstinence in a naturalistic setting while using either nicotine or placebo gum. METHODS: Double-blind, randomised, placebo-controlled study in which 132 dependent smokers abstained for 6 h with the assistance of either nicotine (2 mg, n = 42 or 4 mg, n = 24) or placebo (n = 66) gum while travelling on a non-smoking train. Outcome measures were ratings of craving and mood withdrawal symptoms prior to treatment and at regular intervals during abstinence. RESULTS: In a multivariate analysis of all symptoms, there was no interaction between treatment and time [F(21,110) = 1.28, p = 0.20, [Formula: see text] = 0.20] nor an effect of treatment [F(7,124) = 0.45, p = 0.87, [Formula: see text] = 0.03]. There was an effect of time [F(21,110) = 11.59, p < 0.001, [Formula: see text] = 0.69) and univariate analyses revealed that the majority of symptoms increased linearly throughout the period of abstinence with detectable onsets typically between the first 60 and 180 min of abstinence. CONCLUSIONS: Smokers who temporarily abstain in naturalistic settings experience craving and withdrawal symptoms that emerge linearly over the first 6 h of abstinence. Changes in craving and several mood withdrawal symptoms can be detected within the first 3 h. Nicotine gum may not have an acute effect on the development of these symptoms.
{"Chemical": ["nicotine", "Nicotine"]}