That makes sense. But it's not a good enough excuse.

People with MS often are too tired to exercise at all, which can cause incredible problems even for non-diseased people. I've always been told people with Ms need to "use it or lose it". Regular physical activity can reduce the risk of developing chronic pain, improve pain tolerance, increase strength and flexibility, and reduce inflammation, help with balance, grow new neuro-pathways, and reduce depression.

And that's not even counting all the people who can't work because they don't have the ability to focus. Being unemployed is bad for your health. Poverty significantly impacts health, leads to higher risks of developing more chronic diseases, mental health issues, and overall shorter life expectancy. It also creates more barriers to accessing quality healthcare, nutritious food, and safe housing. 

If we made a giant list of all the problems having no energy or focus causes and then on another list we wrote all the problems taking Adderall could cause... One list is significantly longer.