Answer:
The code range T36-T50 for poisonings by, adverse effects of, and underdosing of drugs, medicaments and biological substances can be used as the first listed or principal diagnosis when the reason for admission or encounter is due to the poisoning, adverse effect, or underdosing of a drug, medicament or biological substance. For example, if a patient is admitted to a hospital due to a drug overdose or toxic reaction, the appropriate T code from this range would be used as the principal diagnosis.