Which of the following is NOT an adverse effect of first generation antipsychotics (FGAs)?

First-generation antipsychotics (FGAs) are primarily known for their effectiveness in treating positive symptoms of schizophrenia and other psychotic disorders, but they are also associated with a range of adverse effects. Among the options presented, hyperglycemia is not typically associated with FGAs as an adverse effect.

Gynecomastia, which is breast tissue enlargement in males, can occur due to FGAs affecting prolactin levels. Extrapyramidal symptoms (EPS), which include symptoms like tremors, rigidity, and bradykinesia, arise from the dopamine blockade caused by these medications. Neuromalignant syndrome (NMS) is a rare but serious reaction to FGAs, characterized by severe muscle rigidity, fever, autonomic instability, and altered mental status.

In contrast, hyperglycemia is more commonly linked to second-generation antipsychotics (SGAs), which are known to have metabolic side effects such as weight gain and diabetes. While some individuals on FGAs may experience changes in glucose metabolism, hyperglycemia is not considered a direct or common adverse effect associated with this class of antipsychotics. Thus, it stands out as the correct answer to the question regarding which option is not an adverse effect of FGAs.