What term describes unusual effects from a drug that may include both lack of effect from large doses or unexpected effects from small doses?

The term that accurately describes unusual effects from a drug, including both lack of effect from large doses and unexpected effects from small doses, is idiosyncrasy. Idiosyncratic reactions are unique to the individual and can manifest as atypical responses to medications that are not predicted based on the drug's known pharmacological action. This can lead to an absence of efficacy in patients who may be tolerant or who metabolize the drug differently, as well as to unexpected effects even when doses are within the expected therapeutic range.

Tolerance refers to a phenomenon where increasing doses are required to achieve the same effect due to the body's adaptation to the drug over time, but it does not encompass the unexpected or unusual reactions described. Side effects are known secondary effects that can occur with almost any medication but are generally predictable based on the drug’s pharmacological profile. Adverse reactions are undesirable effects that occur at normal doses and can often be anticipated, but they do not include the idiosyncratic responses that characterize this question. Therefore, idiosyncrasy is the most fitting term for the described scenario.