Opium & The Kung Fu Master (1984).
Ignore imdb trying to tell you that this movie is called the Lightning Fists of Shaolin. This alternative title is much more fitting, albeit a little on the spoiler side of descriptive.
There is a town, and the town is protected from dubious moral acts and outright evil by the resident Kung Fu master, who has a dutiful if a bit over-excitable student. There are some shady sorts who would like to start importing opium in bulk and cutting it with a bulking agent so that they can lower the cost significantly enough that the average labourer will be able to frequent the establishment. But how could they defeat the kung fu master, to enable them to carry out this plan?
By getting him addicted to opium, it turns out.
Extraordinarily this narrative doesn’t take the route of least resistance when it comes to the main plot. The quest that the hero has to go on is not one of revenge for his master, but revenge for his student. Along the way he must struggle to break his addiction, and only the fates of those who have endeavoured to help him all the way through will ultimately give him the willpower that he needs to make it to the final boss fight of the movie.
This was a surprisingly good movie with some very decent camerawork. The only real negative was that some of the fight scenes were sped up (noticeably) and it really didn’t need that at all.