Question: which category of drugs includes many substances that are chemically similar to neurotransmitters
[{'answer': 'receptor agonists', 'provenance': [{'wikipedia_id': '21865', 'title': 'Neurotransmitter', 'start_paragraph_id': 55, 'start_character': 967, 'end_paragraph_id': 55, 'end_character': 984, 'bleu_score': 1.0, 'section': 'Section::::Drug effects.\n'}]}, {'provenance': [{'wikipedia_id': '21865', 'title': 'Neurotransmitter', 'start_paragraph_id': 55, 'start_character': 0, 'end_paragraph_id': 55, 'end_character': 1577, 'bleu_score': 0.9059370218617501, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13669362443451395981}, 'section': 'Section::::Drug effects.\n'}]}]