The number of Mainers who fatally overdosed the first three months of 2018 was slightly lower than during the same period last year, although the number of fatalities due to the highly potent opioid fentanyl increased, according to the attorney general’s office. Eighty-six people died from drug overdoses in the first quarter of 2018, as compared with 89 who died in first quarter of 2017, according to a report released Friday by the AG’s office.