A Study Exploring Changes in a Variety of Biomarkers Following Dosing With MT1988 in Participants at Clinical High Risk for Psychosis

The goal of this clinical trial is to learn how tests undertaken by people at high risk of developing psychosis (aged 17 to 30 years old) change when those people are given the study drug MT1988 daily for 8 weeks. This will help identify tests that could be used in later trials developing treatments for symptoms in people at high risk of developing psychosis, to measure whether those new treatments are effective. The main question this trial aims to answer is: Can any of the tests (biomarkers) used in this study detect changes in participants dosed with one of two different dose levels of MT1988? Researchers will compare the results from two dose levels of MT1988 to a placebo group. Researchers do not expect to see the test results change in participants taking placebo and this will be compared to changes expected in test results in participants taking MT1988. Participants will: * take a dose of MT1988 or placebo twice per day for 8 weeks * attend clinic appointments every two weeks to undertake assessments * report any side effects they experience to the researchers