Hi Kathy,
Early studies of melatonin suggested that it might stimulate the immune system. Newer studies show that it's more of an immunomodulator with potent antioxidant properties. Melatonin is being used in studies of breast cancer because low melatonin levels have been found in patients with breast cancer. For this reason, night shift work, which causes low melatonin levels, is now considered a risk factor for breast cancer.
In her article on autoimmune diseases, Dr. Shari Lieberman recommends using melatonin as a dietary supplement. The usual recommended dose is 1-3 mg used before sleep. There was an article in Life Extension this year describing studies using higher amounts, but it's always good to start with the lowest dose that's needed.
The herb valerian is also safely used in Graves' disease to induce sleep. Tylenol pm works, but many people find that using 1/2 of one tablet (12.5 mg diphenhydramine) is adequate. Higher doses can have an opposite effect and cause insomnia. Many people with Graves' disease are also sensitive to caffeine and find they can't drink beverages with caffeine after 4 pm.
I hope some of these suggestions help. I've been taking melatonin for the last 15 years with no ill effects. Best, Elaine