The most common though that I see in BJJ is the cervical sprain or strain. The cervical spine is the most mobile segment of the spine however it puts it at a high risk of injury. Cervical sprains/strains are soft tissue injuries. A strain is linked to muscle, while a sprain is linked to tendons.
However, for some people, effects are much shorter and they have to take modafinil 2X per day (albeit this is not that common). For other people, effects can last 20-24 hours. It all depends on how your body processes it.
I've been really frustrated I can't find a reputable source on how long Adderall IR (the instant release that's available in both brand-name and generic forms) lasts. My doctor said 8-10 hours but most people seem to say 3-4 hours. I get up at 6:30 am and go to bed at 11:00 pm, and I need the medication from 7:00-11:00 pm, that's a time period of 16 hours. If the medication lasts only for 3-4 hours, then I'll need to take the medication 4 times a day...