The human body consistently takes this tack when it senses an overload of a natural substance. For example, if you continually take large amounts of cortisone, a synthetic adrenal hormone, your own production of natural adrenalin will stop and your adrenals will gradually atrophy. Likewise taking thyroid will shut down your own natural thyroid production. Thus it stands to reason when you flood your brain with inordinate amounts of serotonin, the same sensing mechanism will begin to shut down some of your serotonin receptors (as happened in animal trials) in an attempt to control the overload. We don't know if they ever reactivate. We do know that organs like the thyroid and adrenals do not restore themselves.