The long-term effects of opioids derive from the fact that continuous use of the drug leads to increased tolerance levels. This means the body would adapt to the current dosage, and so the individual would then require a greater dosage of the drug to obtain the same feeling of high or pain suppression. The nervous system gets so used to the drug that it tells the body that it can no longer survive without the drug. This leads to drug dependence and consequently, addiction.
When the drug is then discontinued, the body has to struggle to adjust, and then withdrawal symptoms are suffered. These withdrawal symptoms may include insomnia, restlessness, jittery nerves, diarrhoea, vomiting, cold flashes with goosebumps, muscle and bone pain. So many cases of death have been reported due to prolonged use of opioids. In 2016, opioid overdose resulted in the death of 1.7 in 10,000 people in the United States.
However, opioids do not cause any organ toxicity as with some other painkillers like aspirin and paracetamol.