What may impact a subject’s performance on field sobriety tests apart from alcohol?

The correct choice highlights how medical conditions and medications can significantly affect a subject's performance on field sobriety tests. Various medical conditions, such as neurological disorders or vestibular dysfunction, can impair balance, coordination, and cognitive function, which are critical for completing these tests effectively. Certain medications, particularly those that are sedating or affect motor skills, can also hinder a person's ability to perform tasks that require physical dexterity and mental clarity.

While other factors like asthma and allergies can affect a person’s overall well-being, they typically do not have as pronounced an impact on the coordination and cognitive tasks assessed during field sobriety tests. Age and weight might influence physical performance to some degree, but they are less direct predictors compared to specific medical conditions or the effects of medications. Hunger and fatigue can indeed affect a person's concentration and energy levels, yet they do not directly relate to the physical impairments necessitating a focus on medical issues and medications in this context.