Final answer:
Lithium is the mood stabilizer that faced slowed acceptance due to overdose poisonings and its status as a basic element that couldn't be patented, impacting its medical adoption.
Step-by-step explanation:
The mood stabilizer whose acceptance was slowed by a series of overdose poisonings and by the fact that the drug is one of the basic elements and could not be patented is lithium. Lithium has been used effectively as a mood stabilizer, particularly in the treatment of bipolar disorder, but it presents challenges in terms of therapeutic monitoring due to its narrow therapeutic index. The inability to patent this basic element also influenced its uptake in the medical community.