Currently those diagnosed with lifelong conditions such as ADHD and those on the autistic spectrum have to pay for prescriptions. These medications are often not a choice, but a necessity. Please consider adding them to the existing medically exempt groups of illness and conditions.
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Part of ADHD means you can be badly organised and struggle with structure. Removing the charge will reduce barriers to getting the medication in the first place. Without medication many struggle to function daily. While there are other benefits a person may get which could pay for the medication, that requires the adult to have applied for them and got them! Make them exempt from prescription charges and you’ll be certain to help these people.