Traces of THC in the blood are enough for a conviction. Here is a typical summary penalty order the first time. Again, it already costs over 3,000 francs, plus there is an entry in the criminal record.

Here it is a bit more favorable, but still: 2'500 francs. Decisive for the punishment was driving under drugs, which is a misdemeanor. Cultivation and possession for personal use, on the other hand, is a trifle (contravention).