Why doesn’t Vyvanse work for so many people?

I was on Adderall for years then switched to Vyvanse. I’m on 40 mg, and even with my tolerance, it still works great.

I get that initial amphetamine kick after an hour, but then it’s smooth coasting for 10-12 hours. The kick wears off and I get a tiny dip, but that’s usually because I need to eat. The effects are subtle, but I notice them whenever I’m doing tasks and able to commit to them.

I sleep great too and I don’t really notice my medication wear off much. I think that also has to do with my routines and systems I built while on medication.

I’ve also found it of course kicks in faster on an empty stomach, but also it lasts just as long when I eat breakfast with it.

I always see people posting about their Vyvanse not working more than seeing it work. I’m just wondering why that is?

I saw another person state that some people are chasing the initial “kick,” which I can understand can apply to some and taking vitamin C prior to dosing.

But I also start to wonder what other reasons could apply as to why this medication doesn’t work.

TLDR: What are some reasons Vyvanse may not work for someone besides dosage or trying a different medication? Genuinely just very curious on different perspectives and experiences.