You can increase your serotonin levels by altering your diet. I know there are some books on this but can't think of any titles.... The basic idea is to eat plenty of COMPLEX carbs (like rice and potatoes, instead of simple carbs like white bread and sugar) and especially in combination with fish or poultry. If you don't eat meat, I'm sure there are some vegetarian sources of the same proteins or amino acids or whatever is the crucial thing.
Sorry to be so vague, but I wanted to get the idea of dietary factors out there!
Mama to a boy EnviroKid
10 years old and a little girl EnviroBaby
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