50-100 milligrams. Try that first.
If you try that and experience no effects, you can try up to 200mg- but I strongly suggest you not go over that.
Absolutely no more than 300-400mg IN A DAY.
This substance can be much more dangerous than it's given credit for. Not only does it decrease the seizure threshold (it can cause seizures), but it also carries the risk of serotonin syndrome- especially when combined with any serotonergic. So absolutely avoid using this drug if you're on antidepressants.
Use with caution.
-PA