i have never taken subutex or suboxone, i'm on methadone. however, i did a lot of reseach on suboxone for my ex so i have a little info.
subutex is suboxone without the naloxone. naloxone causes you to go into immediate withdrawals if u try to abuse it, like shoot it. it is an antagonist, meaning it is a drug that blocks opioids by attaching to the opioid receptors with out activating them. it causes no opioid effect. subutex is buprenorphine. it's a semi-synthetic opioid. it is called an opioid partial antagonist. this means it's maximal effects are much less than those of methadone or heroin, which are full antagonist opioids. it has a higher affinity than other opioids, meaning it will fight for a receptor and win. it will "knock off" other opioids and occupy that receptor, blocking other opioids from attaching to it.
as far as being at day one, since it's a partial agonist rather than a full agonist, i think you could be okay as long as you only took it for a few days during which u would be withdrawing. i used to do the same thing with methadone and it worked for me, my only problem is is i have a muscular disorder and the pain was so great that i would just start doing pills all over again because my back hurt.
anyway i'll be on here again later. hope this helps!