In contrast to mirtazapine, the SSRIs, SNRIs, MAOIs, and some TCAs increase the general activity of the 5-HT, 5-HT, and 5-HT receptors leading to a host of negative changes and side effects, the most prominent of which including anorexia, insomnia, sexual dysfunction (loss of libido and anorgasmia), nausea, and diarrhea, among others.