Taking medications as prescribed is a very important part of managing MS. Some studies, such as this one from NCBI indicate alarmingly low levels of adherence to disease modifying therapies (DMTs).
This article by the National MS Society in the US lists some commonly stated reasons why people stop taking medications, including side effects and dislike of needles.
If you are having problems taking medications as prescribed and/or you are experiencing side effects, you should discuss it with your Neurologist or MS Nurse. Most of the pharmaceutical companies also provide support services for people taking their medications. This may be a visiting nurse service, or a telephone information line. Your MS Nurse or Neurologist should be able to provide you with information and referrals for these services.
This piece provides some guidance on factors to consider in managing MS medications, including a template form to complete to bring to an appointment to review medications
MS & Me Blogger Joan Jordan wrote a piece on the various ways that you can report side effects and the importance of doing so.