 On the day before starting the treatment Day 0 and on the last day of treatment Day 7 participants will be asked to collect saliva sample to measure cortisol levels. Collection of samples will be performed by participants in their own home and is non-invasive. Participants will be provided with appropriate collection vessels containing a cotton swab. They will be asked to roll this swab around in their mouths for a minute after waking and take 4 further samples at 15 minute intervals, each on a separate cotton swab. The cotton swabs will be put back in the collection vessel and participants will be asked to store their saliva samples in the freezer and bring them back to the researcher on the day of testing. 