The results strongly suggest that the mechanism of depression after alcohol drinking may be related to serotonin.

We examined tryptophan and serotonin (5-hydroxytryptamine) levels in the blood after consumption of alcohol. Forty-five minutes after drinking, whole blood serotonin concentration was significantly reduced, whereas no changes were observed in tryptophan level. The diurnal rhythm of 5-HT in subjects who the day before had drunk alcohol was quite different from the control group, but very similar to that of patients with depression. The results strongly suggest that the mechanism of depression after alcohol drinking may be related to serotonin.

The important thing with serotonin, is to keep it at steady levels.

The important thing with serotonin, is to keep it at steady levels. The medicines that raise the level of serotonin in the brain do so by slowing the absorbing of serotonin. Alcohol increases the available serotonin for a bit and then it drops off quickly, leaving the depressed person feeling worse, and they tend to not take the medicine correctly when they feel badly or are drunk. High serotonin levels do not mean somebody will feel happy or good, It makes it more likely that they won't feel really bad.