There are very few reports regarding negative health effects due to Kratom and the circumstances reported were in conjunction with additional illegal substances combined, so there is no conclusive data showing Kratom as the cause for any negative effects.
Health problems are unlikely unless one is consuming large quantities of Kratom every day.
In Thailand, where many of the indigenous population use Kratom daily, those dependent on it can develop weight loss and have physical withdrawal symptoms when quitting abruptly. If any, the withdrawal symptoms may include muscle aches, irritability, crying, runny nose, diarrhea, and muscle jerking. Health problems are unlikely to occur in occasional Kratom users.
Like any drug or medicine, moderation is the key and individual’s reactions may vary. It is uncommon, but an individual could possibly experience an allergic or other unusual reaction to Kratom, even if used responsibly. More commonly, when using an excessive amount, an individual’s body would simply reject the substance, thus as a natural physiological reaction, may experience emesis (Vomiting) as the body’s way of preservation.