Upping the dose doses not help with tolerance, really-there are only so many H1 receptors in the CNS, and past a certain dose, it maxes out, and begins having it?s atypical antidepressant properties and even some anti-psychotic
Lower your dose, then skip a day or for a tolerance break; then try maybe 50mg as a hypnotic -alone-
And you can?t really take it every night; most nights, 25-100mg, however you have to skip nights to maintain the full hypnotic effectiveness
Years of use is a long time, any long term effects would be speculative, and more acute effects depend upon details-just do a ?Seroquel taper?(now that is an odd one to type) and cut dose gradually to at least 100mg, and then get to less than 100mg, and skip a night or two, then take your much smaller dose
If you take it for ANYTHING ELSE that is different; do not simply cut your dose in half randomly, though if it is just for sleep, 200mgbis pointless, although it is also enough to have borderline chronic effects, so go down low and slow +with discretion
Even 100mg would be an improvement, and you can even drop 25ng at a time - if you want, itt isn? required or anything ;(