I think they'll find as much success as we have in America with our drug war.  That is, the market will go underground, the various cartels in the world will grow stronger, people who are into drugs will live in fear, drugs will be used as a way to put away otherwise innocent people which the state happens to dislike, and people who would otherwise be innocent will be ripped from their families to serve jail time.

From what I understand about drug addicts, they do them to fill a gap in their lives, where if the gap was there--such as a loving a caring family--they would not take interest in drugs.  Of course, the president of the Philippines is not taking an approach which will help the drug addicts of their central issue, but rather attempts to use fear as a method of stopping the negative behavior, much as a parent might spank their child or a dog owner may rub the dog's nose in the mess it has made.

Through this approach, the Philippines will never be drug free.  The drug users will always be underground, and the misery created by the drug war (imprisonment removes mothers and fathers from the family after all, as well as gang violence within the black market) will create more druggies.  I predict the drug problem will grow, which will require more and more power to combat the drug problem by the means the president has taken: an endless loop.  The drug war cannot end, and the stated goal of the drug war can never be met.

There are ulterior problems which need to be helped for the drug problem to be resolved (and even then perfection cannot be achieved): the happier the nation is, the less often people will resort to drugs--why would they need to, if they were already doing well?  I'm sure the president of the Philippines means well, and thinks of his behavior as tough hard love, but it's going to make the situation worse.