Mephedrone is probably the mildest hard drug until now. LSD is the least damaging drug around, but it will not induce euphoria, pleasant stimulation, and mood lift. Most hard drugs that give a great high are also very harsh on your health, especially on the heart. Mephedrone gives a pleasant high, but it does not punish you by overstimulating your heart. The most common side effect of most stimulants consumed recreationally is cardiovascular overstimulation. Cocaine is the worst. Cocaine exerts its cardiotoxicity not in one but in two different ways. Mephedrone's cardiac effects are mild. My pulse does not accelerate past 100, even when I do it two days in a row. On speed or Coke or meth, after more than 8-9 hours, my heart decides to let me know she is only able to perform her activity. in an erratic manner that lowers her efficiency considerably and increases the likelihood of potentially catastrophic cardiac events. Mephedrone seems to release a lot less norepinephrine and adrenaline compared to Coke, speed, and meth. That seems to explain Mephedrone's leniency towards the heart. If you don't binge for two days or more, your heart will continue its activity without bothering you.