That makes it hard for your doctor to predict your response to a medicine. Older people usually need less of a drug than younger people to get the desired effects and avoid overdoses. Any symptom, such as vomiting, breathing problems, headache, confusion, or drowsiness is severe or long-lasting. Symptoms develop soon after you have started taking a new medicine or after eating a certain food. Symptoms such as forgetfulness, depression, confusion, or fatigue develop slowly over a period of weeks or months.
Some adverse effects take a while to show up.
You suspect that a symptom is related to a combination of medicine and alcohol. The use of alcohol may worsen side effects of your medicines. A mild symptom, such as dry mouth, lessens your pleasure in life. You can have an adverse reaction to a medicine the first time you take it or after years of being on it. You can develop an allergy to a medicine at any point.