Taking more phentermine than prescribed can lead to serious health risks. Overdose symptoms may include confusion, panic, hallucinations, extreme restlessness, nausea, vomiting, diarrhea, stomach cramps, feeling tired or depressed, an irregular heartbeat, a weak pulse, seizures, or slow breathing (breathing may stop). Drinking alcohol-containing beverages may also increase the risk of side effects. These can include dizziness, feeling nervous and excited, headache, hard stools or diarrhea, dry mouth, and lack of ability to sleep.
A decrease in interest in sex or a change in the ability to have sex may also occur. If you take too much phentermine, it is important to seek emergency medical attention right away. You should also call your healthcare provider or local Poison Control Center. While there are no specific dietary interactions with phentermine, it is best to avoid drinking large amounts of caffeine-containing beverages (coffee, tea, cola) or eating large amounts of chocolate while taking this medication.
Caffeine may increase the side effects of phentermine. It is important to take phentermine in the morning as taking it at night can cause insomnia (difficulty falling asleep or staying asleep).
