If you missed a dose, take it, as soon as possible but, if it is already evening, skip the missed dosage. And also, do not ever combine two dosages at once.
If you overdose on phentermine, then, consult your doctor immediately. Overdose or too much phentermine can potentially be deadly.
Moreover, overdose symptoms might include disorientation, panic, hallucinations, intense restlessness, nausea, vomiting, diarrhea, stomach cramps, feeling exhausted or sad, irregular heartbeats, a weak pulse, seizures, or delayed breathing.