 he didnt even know  about the implant until he tried to bite Willow and couldnt. Thus,  there were no experiments or meds for him to remember. Secondly, at  the end of 4.21 "Primeval" after Adam is destroyed, the government  review panel orders the Initiative filled in with cement. So even if  Spike had any reason to remember some sort of helpful medication,  there shouldnt have been an initiative to go back to!