Clinical trial protocols and published trials

The Trials part of the Cochrane Library, also referred to as CENTRAL, contains published trials and published protocols, but also trial protocols from a number of trials registries including ClinicalTrials.gov.

For those, the Trials (CENTRAL) record does not seem to record publications.    Of course, an ongoing trial won't have any, but some records record the existence of results, if not details of  where they were published.

Records from ClinicalTrials.gov are linked from CENTRAL.   Those ClinicalTrials.gov records do have a space for publications from the trial, but that may not always be filled in even if there are publications.

As an example, two COVID trials:

https://clinicaltrials.gov/study/NCT04523571

and

https://clinicaltrials.gov/study/NCT04368728

Neither of these record any publications from the trial (I imagine it is down to the investigators, or whoever registered the trial, to provide that information).    The ClinicalTrials.gov ID is included in PubMed as part of the SI field, so is searchable, and searching for those same two trials: 

NCT04523571[si]

and

NCT04368728[si]

finds publications for both.   Some for NCT04368728 may be about the trial, rather than trial results, but some are definitely results.

If there are no publications of results recorded in ClinicalTrials.gov, and searching the NCT number finds nothing, then perhaps other possibilities are:

Searching PubMed for an investigator and some words from the protocol title.  Although for both above there are no named investigators in the trials protocols records.    

I asked other health librarians via the lis-medical email discussion list and had some extra suggestions, reproduced here with grateful thanks:

- Contacting the authors or investigators to ask for results (what started this exploration was an enquiry from an undergraduate, and I think this would be more than we'd expect of an undergraduate.  But for a researcher, or a PhD student, maybe it's a possibility).

- Searching the author on ResearchGate for publications around the date of the trial.

 - This tool: http://arrowsmith.psych.uic.edu/cgi-bin/arrowsmith_uic/TrialPubLinking/trial_pub_link_start.cgi.  I gave this a go with one trial my student was interested in, and it did give details of some articles, after some minutes, but none of them looked to be the trial results.

- Checking on Google Scholar for items that cite the trial protocol.  If you have access to Web of Science or Scopus, that might be worth trying there too.

 - Looking at preprint servers.  PubMed includes preprints reporting NIH funded results, because they are in PubMed Central.  A quick search of PubMed for covid[ti], filtering to preprint, finds the same number of results as covid.ti. in Ovid Medline, limited to preprint, so I think Ovid Medline includes just those same preprints (we have Medline ALL).