The following factors change the efficacy of a drug within a person’s system:
1. Age (often due to a decrease in GFR therefore a decrease in drug excretion)
3. Condition of the patient and any previous medical illnesses or conditions
4. Individual variation
5. Idiosyncratic and allergic reactions
How a drug or medication will effect a person following ingestion or injection depends of a variety of factors. These should be considered whenever a person potentially overdoses on either a single drug or has a polypharmacy overdose when determining potential effects and treatment requirements.