My husband missed for awhile with no side affects. This is the oral kind. But, if he misses a dose of the tacrolimus, it will immediately start to flair. Once he takes his missed dose, it goes away immediately. They say after a time, the tacrolimus may build up enough to go off indefinitely, but we are not there yet. The tacrolimus seems to be the treatment that works, maybe without the naltrexone, but don't want to go without just in case it's a cocktail of the two. Also, when you do the tacrolimus, it can be tough on kidneys, he has to get constant blood work done to continue getting the prescription.