But there are different "flavors" or formulas in centrum.....so maybe the one in pakistan that you bought was a different formula from the one you got from abroad.
Also, it could simply be placebo effect (Like how homeopathy works). This might sound a little cold hearted, but try this, buy local centrum and give it to him, and tell him that it's US/abroad made (come up with a realistic story). I've tried similar stuff with homeopathy "patients" close to me (mixed up their medicines), they don't know the difference, because they don't know they're mixed.
Also, centrum is a pfizer brand. Pfizer is present in Pakistan. They sell products in low volumes but very very high prices (their own patent drugs).
Also, got a little more info for you:
these are Pfizer distributors :
http://www.pfizer.com.pk/our-distributors
contact the one in your city (lahore?), see what they have to say about centrum (whether its locally made or imported).
edit : you can also call pfizer directly : http://www.pfizer.com.pk/contact-us