Are there long term effects of carnitine?

Improves weight loss: Study done - one group was given 2000 mg of carnitine, and the other a placebo. In the placebo group, the average weight loss after 12 weeks was one pound. In the carnitine group, weight loss averaged 11 pounds. That’s an eleven-fold increase in weight loss, simply by increasing carnitine levels.

Not so much: Probably if you continue taking very large doses for a very long time. But it is relatively safe.