Currently in 2015 it is illegal to possess any amount of Cannabis in Belgium. The old law was that you could possess 3g but it was overturned. Though you are legal to have weed in your posession, you are not allowed to smoke it in public places and especially not nearby minors.
Since Leuven is a city with a high density of students, you can smell weed all over town, especially on hot summer evenings; but the police is always trying to stop people from smoking and they can definately cause problems. The best way to keep yourself from getting caught is by smoking somewhere private or in the woods, park, etc.
Where to buy marijuana in Leuven
Weed can be bought easily around the old market, which is a place with a lot of bars, but you have to be careful because it’s right near the police department. If you cannot find weed there, you can always try talking to some students and you will probably find some weed.
Marijuana prices & types
The prices vary from 4-5 euro’s to 7-10 euro’s per gram which should give you some high quality weed. Most weed is grown locally by in- and outdoor growers, but you also find a lot of shopweed that has been imported from the Netherlands.