Psychiatric disorders are due to 1 of 4 things--chemical poisons (which drugs are) parasites and radiation. Then anything that imbalances the endocrine glands or won't allow the body to absorb enough nutrients in a balanced way--like a clogged up colon or liver--will cause any disease, physical or mental. Drugs will cause ALL this.
Try Omega 3 oil. Then get him to do a good colon cleanse. I recommend Richard Schulze 's Colon Cleanse products, stop the drugs and give him an all around good bunch of supplements that includes Iodine and ionic minerals. Distilled water. You can use topical mag, mag glycinate, or the best suggestion I can think of would be to contact the Pain And Stress Center and employ one of their certified nutritional counselors and have an amino acid panel done. A full spectrum natural B will do wonders. Contact the experts in natural brain chemistry at the Pain and Stress Center out in Texas who work under Dr. Billie Sahley, PhD.