Well it depends on your inclusion of an intervention and how you choose to give the intervention OR are the subjects already taking an intervention by their treating physician. If you choose and randomize who gets the intervention and who does not, then you definitely have to get your study designated as a clinical trial and have it registered.
Additionally, your university may have strict rules about studying intervention efficacy no matter whether you dispense the intervention or not. so, you will need to double check with your Office of Sponsored Projects and your IRB.
According to ClinicalTrials.gov you can use their check sheet to determine if any of your studies need to be registered. The title of this document :
Checklist for Evaluating Whether a Clinical Trial or Study is an Applicable Clinical Trial (ACT) Under 42 CFR 11.22(b) for Clinical Trials Initiated on or After January 18, 2017
I hope this helps you with decision-making.
Best regards,
Dr. Nejtek,
Associate Professor, UNT Health Science Center in Fort Worth, Tx