The effects of kratom depend on the dosage used; stimulating effects occur at a low dosage, while at higher dosages an effect similar to opiates is observed. This can be shown in man as well as animals. The dosage determination for the borderlines of stimulating, analgesic, or toxic dosages is admittedly extremely (weil es genormte Personen nicht gibt) difficult. Mitragynine has in addition a cough alleviating, anti-nociceptive and diarrhea relieving effect, which is comparable to codeine (Suwanlert, 1975).
The effect also depends on the quality of the kratom (there appear greater differences to exist) and the dosage taken which generally is less than 5 or more than 20 g (0.176 to 0.705 ounce). Often the effects are compared with those of opiates, which are mainly subjective assessments. The effect starts generally after 10 to 20 minutes and increases up to one hour after oral application. The primary effects mostly last between 3 to 6 hours. The stimulating as well as sedating effect is described among them, although it is mentioned to last longer.
Side effects like nausea, vomiting, and diarrhea are often observed symptoms in the use of kratom, while nystagmus and trembling count to the more seldom side effects. In chronic use sometimes loss of appetite and weight, hyperpigmentation, dark stool of small amount, constipation, frequent urinations, dry mouth and psychoses occur (Grewal 1932). The loss of weight could be connected with the reduced 2-deoxy-D-glucose stimulated production of the stomach, which is followed by a loss of appetite. This can likewise be observed when taking morphine (Tsuchiya et al., 2002).
Frequent and long term use can also lead to addiction symptoms. In 1957 Thuan documented the first case of a man addicted to kratom, he never had increased his consumption, was in good health and psyche, and was not emaciated. After withdrawal he showed obvious withdrawal symptoms like aggressions, sadness, running nose, bone and muscle pain, and jerky movements. Bodily withdrawal symptoms normally last four to five days and disappear then completely (Jansen and Prast, 1988).
Kratom is according to the Micromedex Poisindex from a dosage of 50 mg pure mitragynine on toxic and evokes motor excitability, nausea, convulsions of the face, tongue, and extremities as well as being unable, to keep the balance with feet put side by side and eyes closed. On the other hand Macko et al. (1972) reported that mice up to 920 g / kg (32.5 oz / 2.2 lb) showed no toxic signs.