How to get a fake study into Pubmed

  1. Find a predatory journal that made it into Pubmed Central for whatever reason
  2. Submit and pay for your article
  3. Voila, Pubmed will list your predatory study.

This is what I learned this week when writing to the Pubmed help desk

Hi ….,
Thank you for writing to the help desk. Content added to PubMed from PMC comes from two sources: journals that overall have met NLM’s standards for PMC (https://www.ncbi.nlm.nih.gov/pmc/about/guidelines/#sciqual); and author manuscripts deposited in compliance with the public access policy of NIH or other collaborating funders.
NIH and other funders do not dictate the journals in which their funded authors may publish. This particular author manuscript, the single citation from this journal appearing in PubMed, was deposited in compliance with the public access policy of NIH (https://publicaccess.nih.gov/).
Kind regards,

U.S. National Library of Medicine

Unfortunately, I am not the first one to notice the decline of Pubmed. scholarlykitchen.sspnet.org has written about that before

What is PubMed? Is it a search engine? A credentialing system? A filter? Is it a publisher? An enabler of open access (OA) publishing? A technology provider? A competitor? Depending on the situation, you can answer each of the above in the affirmative, despite the contradictions many of the combinations may cause.
Twenty years ago, PubMed was a credentialing system, an online port of the MEDLINE index. This shift of medium quickly made it a search engine, but one built on a manual and highly curated index ….
Now, a new twist is emerging, and that seems to be that PubMed may be consciously or unwittingly acting as a facilitator of predatory or unscrupulous publishing.

see also the-scientist.com

If a predatory journal is confined on its website, which is often of low-quality, the chance that patients or scholars will read and cite these articles is very low,” says Andrea Manca, a professor of physiology at the University of Sassari in Italy. “The problem is that when they are displayed in the most popular biomedical database that we have, there are many [people] who think if a journal is on PubMed, then it is fine—which is not true, unfortunately.

and there is even a Pubmed listed paper

Finally here is a more recent email from a predatory journal, that wrote to me “we pleased to find a reputed personality in the filed of Medical Research” (sic!)