I couldn't tell you but i can tell you that 8 hits a day is too much. Even assuming they are small 25mg shards per hit that equals 200mg a day, which seems to me like quite a bit of meth.
You don't have to ween off meth, there will be minor physical withdrawals like excessive fatigue but it's mostly going to be psychological and tapering won't help with that. If you want to stop get some healthy food, plenty of water, and plenty of rest. It might be a difficult week but it'll be well worth it in the long run.