There are side effects that may be present with Gravol usage. Minor adverse reactions that may be experienced by a patient include the following: sleepiness, abdominal pain, nausea, an increased appetite, rapid weight gain, dry or scratchy throat, headaches, or a thickening of a patient's mucus. More serious side effects that could be a sign of an overdose and may necessitate immediate medical intervention are an impairment of motor skills, faintness, hallucinations, insomnia, difficulty breathing, or seizures. If any of these adverse reaction are exhibited by a patient, a local doctor should be contacted as soon as possible.