What permanent side effects of smoking weed are there?

Cognition & emotion. Thc dulls mentation and distorts mood; some people are especially vulnerable and develop minor major paranoid states. Repetition of these mental states just by itself tends to embed them making them harder and harder to reverse (and to reclaim "lost" time). In vulnerable people, thc can trigger overt mental disorder that can be lifelong. Best to avoid in spite of opo approval.
Unknown. What's important is some of the short term effects which are well studied including difficulty with driving due to slow responses and cognitive slowiing.