Q:

How do we relate Adverse Reactions and Drug in Open FDA?

I have been trying to relate adverse reaction to list of drugs in the Open FDA JSON but just can't manage to understand.
Consider this JSON:
     "reaction": [
      {
        "reactionmeddrapt": "DERMATITIS"
      },
      {
        "reactionmeddrapt": "FEBRILE NEUTROPENIA"
      }
    ],
    "patientonsetageunit": "801",
    "drug": [
      {
        "drugauthorizationnumb": "18057",
        "drugcharacterization": "1",
        "drugstartdateformat": "102",
        "drugindication": "NON-SMALL CELL LUNG CANCER",
        "medicinalproduct": "CISPLATIN",
        "drugadministrationroute": "042",
        "drugstartdate": "20050628",
        "openfda": {
          "unii": [
            "Q20Q21Q62J"
          ],
          "spl_id": [
            "fd135112-4330-42bd-ac2e-d3cd6f96325d",
            "c26e5c72-fcb2-4eda-80e2-6b056a194c3a",
            "2bf8d2fb-80c8-401d-8e9b-d58463f5e954",
            "64db63dd-9e65-4c4e-937f-09a8ae9dcfab",
            "d3e05034-cd9e-4dac-8c71-21f27772bf5e",
            "b4c79396-7cbf-44db-9ec6-c72b4b380443",
            "601e6d97-95d4-4ef8-9c70-1abdb57e3df3"
          ],
          "product_ndc": [
            "44567-510",
            "63323-103",
            "44567-509",
            "0703-5747",
            "0703-5748",
            "61126-004",
            "61126-003",
            "0069-0084",
            "67457-425",
            "67457-424",
            "0069-0081"
          ],
          "substance_name": [
            "CISPLATIN"
          ],
          "rxcui": [
            "205821",
            "309311"
          ],
          "spl_set_id": [
            "64975f5d-0eca-4998-8a72-06eec98285eb",
            "2bf8d2fb-80c8-401d-8e9b-d58463f5e954",
            "a043dd33-3d1d-4884-bb75-80f221e749ba",
            "b2a8e240-5e93-4a58-9ba2-688a87a5e20c",
            "199a6ab3-9b00-49fc-90d4-644d58141235",
            "a440f077-46f6-4688-a209-65bce38d1c92",
            "de6302d5-85f0-4116-a709-57826c2c84fe"
          ],
          "product_type": [
            "HUMAN PRESCRIPTION DRUG"
          ],
          "pharm_class_cs": [
            "Platinum-containing Compounds [Chemical/Ingredient]"
          ],
          "manufacturer_name": [
            "Mylan Institutional LLC",
            "Pfizer Laboratories Div Pfizer Inc.",
            "Fresenius Kabi USA, LLC",
            "Teva Parenteral Medicines, Inc.",
            "WG Critical Care, LLC",
            "Corden Pharma Latina S.p.A."
          ],
          "brand_name": [
            "PLATINOL",
            "CISPLATIN",
            "PLATINOL-AQ"
          ],
          "route": [
            "INTRAVENOUS"
          ],
          "nui": [
            "N0000175073",
            "N0000175413"
          ],
          "package_ndc": [
            "61126-003-01",
            "67457-425-51",
            "61126-004-01",
            "61126-004-02",
            "44567-510-01",
            "0703-5748-11",
            "44567-509-01",
            "0069-0084-07",
            "0069-0081-01",
            "0703-5747-11",
            "63323-103-51",
            "67457-424-10",
            "61126-003-10",
            "63323-103-65",
            "63323-103-64"
          ],
          "pharm_class_epc": [
            "Platinum-based Drug [EPC]"
          ],
          "generic_name": [
            "CISPLATIN"
          ],
          "application_number": [
            "ANDA074735",
            "ANDA091062",
            "ANDA074656",
            "NDA018057"
          ]
        },
        "drugenddate": "20050628",
        "drugenddateformat": "102"
      },
      {
        "drugcharacterization": "1",
        "drugstartdateformat": "102",
        "drugindication": "NON-SMALL CELL LUNG CANCER",
        "medicinalproduct": "GEMCITABINE",
        "drugadministrationroute": "042",
        "drugstartdate": "20050628",
        "openfda": {
          "unii": [
            "B76N6SBZ8R"
          ],
          "spl_id": [
            "90b6ff1e-82b8-4af6-bd5e-7959987161cd",
            "c9981fc3-ae63-483f-bbbf-29de04246233",
            "4d39651e-9634-4600-8e85-a26d59e9fe6a",
            "6e49921e-761e-4e68-864c-c29961fd0d2a",
            "8df4c455-5b17-40a8-ae1d-9d5f86d11727",
            "f63acd13-ba91-4883-b65c-e2dc46a44ffa",
            "d6a4308a-e499-a35b-be95-5f2b05772131",
            "4cef5f77-82b5-ba03-1f26-4fdeb8af63fd",
            "7a2275c5-285c-4c2a-8fdc-159353f3d287"
          ],
          "product_ndc": [
            "0409-0182",
            "0409-0183",
            "0409-0181",
            "0409-0186",
            "0409-0187",
            "55111-687",
            "0409-0185",
            "47335-154",
            "55111-686",
            "47335-153",
            "55390-391",
            "25021-208",
            "25021-209",
            "63323-125",
            "63323-102",
            "63323-126"
          ],
          "substance_name": [
            "GEMCITABINE HYDROCHLORIDE"
          ],
          "rxcui": [
            "1148919"
          ],
          "spl_set_id": [
            "a625c92b-c569-4b98-8d2e-2b3f5e12b34f",
            "6087be15-56c1-4794-b159-ad9082b631b9",
            "d16907e7-a8c8-4039-ace4-cf4e24ba68c0",
            "e18ed1cb-7dd0-4001-bfda-17d1f4587fb8",
            "ffc0a4be-6091-4157-837e-3637c1e121a6",
            "c550dd16-a5e8-44be-87f2-210c15bbb513",
            "eafcebc8-ddef-bb6b-fd0a-9d8b9962cdc4",
            "aa445f68-1e55-a587-76dc-def068bc9c74",
            "dc02a23b-3ff9-4441-aa91-8e9e629a7315"
          ],
          "product_type": [
            "HUMAN PRESCRIPTION DRUG"
          ],
          "manufacturer_name": [
            "Dr. Reddy's Laboratories Limited",
            "Sagent Pharmaceuticals",
            "Hospira, Inc.",
            "Sun Pharma Global FZE",
            "APP Pharmaceuticals, LLC",
            "Bedford Laboratories"
          ],
          "brand_name": [
            "GEMCITABINE HYDROCHLORIDE",
            "GEMCITABINE"
          ],
          "route": [
            "INTRAVENOUS"
          ],
          "nui": [
            "N0000000233",
            "N0000175595"
          ],
          "pharm_class_moa": [
            "Nucleic Acid Synthesis Inhibitors [MoA]"
          ],
          "package_ndc": [
            "0409-0181-01",
            "63323-125-53",
            "25021-209-50",
            "0409-0182-25",
            "55390-391-10",
            "0409-0182-01",
            "63323-102-13",
            "55111-687-25",
            "0409-0183-01",
            "55111-686-07",
            "0409-0185-01",
            "25021-208-10",
            "47335-154-40",
            "55390-391-50",
            "0409-0186-01",
            "0409-0181-25",
            "47335-153-40",
            "63323-126-03",
            "0409-0187-01",
            "0409-0183-25"
          ],
          "pharm_class_epc": [
            "Nucleoside Metabolic Inhibitor [EPC]"
          ],
          "generic_name": [
            "GEMCITABINE",
            "GEMCITABINE HYDROCHLORIDE"
          ],
          "application_number": [
            "ANDA079183",
            "ANDA079160",
            "ANDA090799",
            "NDA200795",
            "ANDA078433",
            "ANDA091365",
            "ANDA078339"
          ]
        },
        "drugenddate": "20050628",
        "drugenddateformat": "102"
      }
    ]

Here, each patient has a list of adverse reactions (CEREBROVASCULAR ACCIDENT & TRANSIENT ISCHAEMIC ATTACK) and list of drugs which caused it (CISPLATIN, GEMCITABINE and many more). But nowhere can I find which drug has caused a particular reaction as reactions and drugs are maintained in a separate list.
So is it possible to deduce this relation?
The endpoint URL is: 
https://api.fda.gov/drug/event.json?search=receivedate:[20040101+TO+20140104]&limit=1&skip=3009

A:

There is no way to make the connection you seek using the data in the openFDA drug adverse events API. Reports include all suspected adverse reactions, and all known drugs the patient was taking. While the classification of drugs as suspect or concomitant may be helpful, it is not always present, and it is often impossible to know which drug caused a specific reaction, or whether a drug caused the reaction at all. A suspected adverse reaction may actually be part of a course of illness.
The documentation at https://open.fda.gov/drug/event/#adverse-event-reports clearly states:

A report may list several drug products, as well as several patient reactions. When a report lists multiple drugs and multiple reactions, there is no way to conclude from the data therein that a given drug is responsible for a given reaction.

