Are the results of this harm study valid?

Were there clearly defined groups of patients, similar in all important ways other than exposure to the treatment?
Were treatment exposures and clinical outcomes measured in the same way in both groups?
Was the follow-up of study patients complete and long enough?
Do the results satisfy some "diagnostic tests for causation"?
- Is it clear that the exposure preceded the onset of the outcome?
- Is there a dose-response gradient?
- Is there positive evidence from a "dechallenge - rechallenge" study?
- Is the association consistent from study to study?
- Does the association make biological sense?

Reference: Evidence-based Medicine - Sackett, Richardson, Rosenberg and Haynes.