I read that big doses of Vitamin D help some people. If you haven't tried that yet, it would be worth researching and talking with your doctor. Don't just take my word for it.
TimC
Just another thought, did you try Prozac? Prozac is not a substrate of Pgp (P-glycoprotein). This protein is encoded by the ABCB1 gene, non-responders often have a genetic mutation in this gene which can greatly modulate the concentration of several antidepressant that are substrate of Pgp. This genetic mutation is often responsible of the non-responding effect of several antidepressants.
Unfortunately not a lot of doctor are aware of this and they goes trials and errors before trying Prozac which is, like I said, not a substrate of Pgp. So there you have it, I would try Prozac and see if the Pgp protein is the problem.
Any decision regarding switching, adding modification of dosage in medications, whether it be supplements or prescription drugs must be addressed with a qualified physician.
M4
This is from PubMed:
Abstract
Sixty percent of cases of clinical depression are considered to be treatment-resistant depression (TRD). Magnesium-deficiency causes N-methyl-d-aspartate (NMDA) coupled calcium channels to be biased towards opening, causing neuronal injury and neurological dysfunction, which may appear to humans as major depression. Oral administration of magnesium to animals led to anti-depressant-like effects that were comparable to those of strong anti-depressant drugs. Cerebral spinal fluid (CSF) magnesium has been found low in treatment-resistant suicidal depression and in patients that have attempted suicide. Brain magnesium has been found low in TRD using phosphorous nuclear magnetic resonance spectroscopy, an accurate means for measuring brain magnesium. Blood and CSF magnesium do not appear well correlated with major depression. Although the first report of magnesium treatment for agitated depression was published in 1921 showing success in 220 out of 250 cases, and there are modern case reports showing rapid terminating of TRD, only a few modern clinical trials were found. A 2008 randomized clinical trial showed that magnesium was as effective as the tricyclic anti-depressant imipramine in treating depression in diabetics and without any of the side effects of imipramine. Intravenous and oral magnesium in specific protocols have been reported to rapidly terminate TRD safely and without side effects. Magnesium has been largely removed from processed foods, potentially harming the brain. Calcium, glutamate and aspartate are common food additives that may worsen affective disorders. We hypothesize that - when taken together - there is more than sufficient evidence to implicate inadequate dietary magnesium as the main cause of TRD, and that physicians should prescribe magnesium for TRD. Since inadequate brain magnesium appears to reduce serotonin levels, and since anti-depressants have been shown to have the action of raising brain magnesium, we further hypothesize that magnesium treatment will be found beneficial for nearly all depressives, not only TRD.
I also came across a search that said the FDA approved a drug for TRD.
Don't know what treatments your doctor / psychiatrist has tried, but the following link may be of help. Have you ever tried CBT or similar programs?
http://www.mayoclinic.com/health/treatment-resistant-depression/DN00016