Your friend is most likely going to experience some moderate withdrawal
symptoms. The tapering off will help.
Your friend should expect to feel these symptoms:
Diarrhea, irritability, insomnia, muscle/joint pain and general malaise.
Your friend should stock up on these otc comfort meds:
Imodium ad green liquid or loperimide pills for the diarrhea
Ibuprofen for the muscle aches
for anxiety and insomnia
Multivitamins to help his depleted system
Sports drinks full of electrolytes
It may be 2-3 days of hell then 2-3 days of readjustment after that but your friend should be back on his feet in no time
Keep reading the forums there is much valuable information on here about your friends situation.
Best of luck