Case series
A description of outcomes in a group of patients who received a treatment. No control group, no randomisation, usually retrospective.
Useful for generating hypotheses and describing safety signals. Not capable of establishing that a treatment works, because there is nothing to compare against.
Registry
A systematic ongoing collection of data on patients receiving a treatment in routine practice. Larger than a case series, often long-running, and valuable for detecting uncommon adverse events over time.
Registries reflect real-world use, which is a genuine strength. But participation is typically voluntary and enrolment is not randomised, so registries cannot establish efficacy either. A registry is not a trial, and describing enrolment in one as participation in a study can be misleading.
Clinical trial
A prospective study with a defined protocol, pre-specified endpoints, and usually a control group. Randomisation removes selection bias; blinding removes expectation bias.
Registration on a public trials register before enrolment is standard practice and allows the pre-specified endpoints to be checked against what was eventually reported.
Why the distinction matters commercially
Patients are sometimes told they are joining a "study" when enrolling in a registry, occasionally while paying for the treatment. Paying to receive a treatment and having your outcome recorded is not the same as participating in a clinical trial, and it is reasonable to ask directly which one is being offered.
This article covers general science and published research. Whether any approach is appropriate for you is a clinical question, answered by a licensed provider through a good-faith exam.
Movera Wellness Institute. Medical services are provided by licensed California practitioners. Supervising physician: Dr. Arnold S. Kremer, DO (CA license #20A4242).