Isoprinosine and weight gain (Immunovir, Viruxan, ecc.). any suggestion ?

Padova, Italy
Hi to all.
I'm at the fifth month of Isoprinosine (in Italy it's called Viruxan, in other countries Immunovirs) , at the dosage of 500mg twice a day (every 8 hours) for 45 days and then for 15 days off, for a year.
It causes me more drowsiness and for sure it's the cause of my weight gain.
It's a not usual effect but i'd like to have some help from you . What could be the cause ?
I'm not the only one with this problem (see this post for example) .

Anyone has a suggestion to get some exams to see what is happening ? Thank you !!!