Why do I retrieve zero results when searching for combination drugs whilst using an AND in the same search statement in Embase or Medline?
 


It is common practice on the Dialog platform when searching a multiplicity of Embase or Mesh thesaurus terms to be able to combine them together to make a more simplified search step.

Thus, instead of running a search:

Emb.exact(“acetylsalicylic acid”) or emb.exact(“paracetamol”) or emb.exact(“ibuprofen”)

You can instead search:

Emb.exact(“acetylsalicylic acid” or “paracetamol” or “ibuprofen”)

As illustrated below, the same number of results are retrieved


This also applies if you wish to include the same qualifiers to limit the search:

Thus searching:

Emb.exact((“acetylsalicylic acid”) LNK (ae OR po OR to OR co OR ct OR si OR it)) or emb.exact((“paracetamol”) LNK (ae OR po OR to OR co OR ct OR si OR it)) or emb.exact((“ibuprofen”) LNK (ae OR po OR to OR co OR ct OR si OR it))

Can be made simpler:

Emb.exact((“acetylsalicylic acid” or “paracetamol” or “ibuprofen”) LNK (ae OR po OR to OR co OR ct OR si OR it))

As illustrated below, again the same number of results are retrieved 



However, although the Boolean OR operator works with the LNK operator to combine Embase or Mesh terms together. The same does not happen for the AND operator. This Boolean AND would be used for searching combination drugs that do not have their own Mesh/Embase thesaurus entry.

Thus, to search for the combination drug paracetamol + diphenhydramine, the above procedure would not work. The same is true if you include or exclude qualifiers

Emb.exact((paracetamol AND diphenhydramine) LNK (ae OR po OR to OR co OR ct OR si OR it))

The above appears to run to completion but delivers zero results

However, if you separate the drugs into their separate search strings:

Emb.exact((paracetamol) LNK (ae OR po OR to OR co OR ct OR si OR it))
Emb.exact((diphenhydramine) LNK (ae OR po OR to OR co OR ct OR si OR it))
S1 AND S2


Results are retrieved:

image.png

To explain: Whereas when using OR Boolean operator, the LNK operator will search for each individual thesaurus term in a record. It does not when using the AND Boolean operator. In this instance it appears to be searching for paracetamol AND diphenhydramine in the same thesaurus term and not searching for paracetamol and diphenhydramine in separate entries in the same record – which is what happens in the example below when combining the  separate search terms: