Hi juls, no you are no supposed to take multivitamins while on TFR. I'm not sure if it will effect your diet, but they are unneccessary and pointless to take regardless. with every vitamin you take, if you take more than your 100% reccommended daily allowance, your body wont keep the extra. like if you take in 120% of the vitamin C you need for the day, your body will basically pee out that 20%! with TFR you are given all of your daily requirements of vitamins and minerals. with the exception of fibre, hence needing to take Fibre Clear. basically, if you take any extra vitamins it will be a waste of your time & money, and may even effect how well your diet works!