First in Human Safety and Ease of Use Assessment of 400mg Progesterone Callavid in Women With Luteal Phase Insufficiency

The aim of this clinical trial is to assess safety of a new vaginal 400mg progesterone drug-device combination product in a first in human trial. Additionally, it aims to assess user acceptability and ability to deliver progesterone. This Phase I trial is a randomised open-label first-in-human crossover trial, recruiting participants who are non-pregnant with luteal phase insufficiency. The main questions it aims to answer are: 1. What are the safety and tolerability profiles of the two progesterone formulations (400mg Progesterone Callavid vs. Cyclogest 400 mg), including the incidence of adverse events (if any) such as allergic reactions, gastrointestinal symptoms (e.g. bloating, constipation), and neurological effects (e.g. headache, drowsiness, euphoria)? 2. What is usability experience for patients using the Callavid drug-device combination compared to pessaries / suppositories (i.e. Cyclogest 400 mg)? 3. How do serum progesterone levels vary within participants when using 400 mg progesterone delivered via the Callavid drug-device combination compared to Cyclogest 400 mg, and what are the implications of this variability for dose-response relationships and future trial design?