Adverse effect of drug/meds/biol subst, init

This code signifies an undesirable or harmful reaction to a drug, medication, or biological substance that was administered correctly and as prescribed. It represents an unintended side effect rather than an overdose or poisoning. This specific code is used for initial encounters when the adverse effect is due to a substance not otherwise specified in more granular codes.

Apply this code when a patient presents for the first time with an adverse reaction to a medication, vaccine, or other biological substance, and the specific substance or type of substance is not detailed in a more specific ICD-10-CM code. Examples include allergic reactions, unexpected side effects, or idiosyncratic responses to correctly administered drugs.

• Always sequence this code after the code for the specific adverse effect (e.g., rash, nausea).
• Ensure the documentation clearly states an adverse effect, not poisoning or underdosing.
• Use this code as a last resort when a more specific T36-T50 code for the substance is unavailable.