Does weed take out or lower your serotonin levels in your brain?

No: Weed which has cannabis does not effect serotonin in the brain in animal studies. Effect in human brain serotonin is not known.

Can't tell: If you could know what you are taking, it would help. But what you are told is weed may be different from other weed, may be cut with something, is not tested for quality control, is sold to you in a chain that may not involve honest people, and may not be what was tested in any government or scientific study. What it does to your brain: anyone's guess.