Amitriptyline is a very well researched anti-depressant and one of the oldest.  It is widely used in low doses for headaches and pain due to its ability to raise the pain threshold.  It is a dual-action anti-depressant, meaning it is probably slightly more effective on average than an SSRI.  Side-effects are excessive sleep, weight gain, dry mouth, constipation, and occasionally dizziness.

Someday, I hope to have time to get more of its research posted here.

8 DB Study Depression with Anxiety Meta-analysis: Mirtazapine vs. placebo in all and amitriptyline in 4. Both meds help decrease anxiety by the same amount. Jan Fawcett, Rush Presby-St Luke J Clin Psychiatry 59:123-7. Mirtazapine causes some weight gain, but amitriptyline causes more.

Helps More than Fluoxetine in AD but Greater Drop Out: DB of 37 patients fluoxetine vs amitriptyline by Taragano of U Buenos Aires in Psychosom 5/97;38:246 found equal improvement in depression on fixed dose protocol but 58% dropout vs 24%.

Average Wt Gain #12: At 9 mo follow-up. Thioridazine, and chlorpromazine also associated with weight gain.

Amitriptyline More Weight Gain Than Desipramine or Nortriptyline: 73 hospitalized depressed patients treated with one of four antidepressants for 1 month. After a 2-week medication-free period, patients were randomly assigned to treatment with amitriptyline, nortriptyline, desipramine, or zimelidine. By the end of 1 month, treatment with all three tricyclic compounds promoted weight gain, with the greatest increase observed during amitriptyline treatment; less weight was gained by patients treated with nortriptyline and desipramine. Zimelidine caused none. Psychiatry Res 1988 Dec;26(3):265-71