Participants allocated to the intervention group will receive access to levidex in addition to treatment as usual (TAU). levidex is a digital health application designed for individuals with Multiple Sclerosis (MS), accessible through a web browser. The application comprises 16 modules, with the majority focusing on treatment methods derived from cognitive behavioral therapy (CBT) and health behavior change. The program operates through interactive "dialogues", which are accompanied by illustrations, audio recordings, motivating text messages, worksheets, and summaries. Users are also encouraged to regularly complete short questionnaires to monitor their complaints. Once registered, the program remains accessible for 365 days.

Participants allocated to the control group will receive an overview of relevant brochures from the Deutsche Multiple Sklerose Gesellschaft (German Multiple Sclerosis Society) on the topic of lifestyle in Multiple Sclerosis (MS) in addition to treatment as usual (TAU). After 6 months, they will be offered access to levidex.

Participants will receive access to the digital health application levidex in addition to treatment as usual (TAU).

The HALEMS measures MS-specific quality of life. It covers the following domains: fatigue, thinking, mobility lower limb, mobility upper limb, communication and mood. The total score is calculated as the average of the scores in the six domains and ranges from 1 to 5. Higher scores represent lower quality of life.

The PHQ-9 measures depressive symptoms. Each of the 9 items is answered on a 4-point Likert scale ranging from 0 (not at all) to 3 (almost every day). The total score ranges from 0 to 27. Higher scores represent higher depressive symptoms.

The HALEMS measures MS-specific quality of life. It covers the following domains: fatigue, thinking, mobility lower limb, mobility upper limb, communication and mood. each domain score ranges from 1 to 5. Higher scores represent lower quality of life.