An overdose (or OD) is defined as taking “an excessive quantity or amount” of a drug, or “too great a dose” of a medication . Ingesting a large amount of phentermine falls under both of these definitions.
The maximum daily dosage for phentermine weight loss pills is 37.5 milligrams. Taking significantly more than this amount in a 24-hour period – or noticeably more than prescribed – is considered a phentermine overdose.
To the surprise of most users, phentermine overdose can either be an acute (short-term) or chronic (long-term) condition .
Yes, it is possible to overdose on phentermine. Taking too much of this drug can prove dangerous and potentially fatal.
Phentermine is a legal and popular weight loss medication, but it is still a powerful central nervous system stimulant and can produce negative effects when conumed in excess. In fact, phentermine and amphetamine have nearly-identical chemical structures; the only difference between these two substances is a methyl group (CH3) on phentermine that replaces a solitary hydrogen (H) on amphetamine [3,4].
Thankfully, this small molecular interchange produces a major biological difference. As a result of this alteration, phentermine is considered a category IV controlled substance as opposed to amphetamine, which is classified as more severe, category II substances [3,4].
Still, phentermine’s effect on the central nervous system remains pronounced and taking too much phentermine can result in a dangerous, or even fatal, overdose – just like overdosing on amphetamines.
How much phentermine it takes to overdose varies widely between individuals.
Drug combinations, previous exposure to phentermine, and biological & lifestyle factors all affect a specific patient’s likelihood of overdose.
Combining other drugs with phentermine significantly increases the risk of a dangerous reaction. Likewise, while new users or people with a low tolerance may be more likely to overdose, even long-term users can overdose on phentermine . For this reason:
It is impossible to predict how a particular person will react to excessive amounts phentermine and aphentermine overdose can be dangerous, or even fatal.
As a central nervous system (CNS) stimulant, this medication activates the sympathetic nervous system in a hormonal cascade similar to "fight or flight" . While modest activation of this system proves beneficial for weight loss because it suppresses appetite and boosts energy, moderation is key.
Taking too much phentermine (or combining this medication with other drugs that increase its effects) can overstimulate the central nervous system and lead to dangerously high blood pressure and heart rate, or even circulatory collapse and death . Overdose of pharmalogically similar compounds, such as amphetamines, can lead to convulsions (seizures) and coma, so this is another concern withphentermine overdose – especially in patients with multiple substances in their systems.
If you suspect you or someone you are with has overdosed on phentermine, call 911 or go to a hospital right away.
If you suspect a phentermine overdose or experience any unusual symptoms after ingesting a high dose of phentermine, call emergency medical services (911) or get to a hospital right away.
Phentermine overdose symptoms include:
Fatigue and depression often follow this heightened state of stimulation .
Always seek professional advice in the case of a suspected phentermine overdose. Do NOT try to treat an overdose at home.
Depending on the severity of the overdose, you may choose to:
If you or someone with you is already displaying phentermine overdose symptoms – or has trouble breathing, seizes or collapses – call 911 immediately .
Treatment for phentermine overdose is largely symptomatic, but should always be directed and supervised by a medical professional .
Learn more about phentermine!
1. Merriam-Webster, Incorporated. (2019). Overdose.
2. U.S. Food and Drug Administration. (2012). Adipex-P (phentermine hydrochloride) capsules label [Brochure].
3. National Center for Biotechnology Information. PubChem Database. Amphetamine, CID=3007.
4. National Center for Biotechnology Information. PubChem Database. Phentermine, CID=4771.
5. Liapko, G. (2019, March 19). How to Recognize a Phentermine Overdose (& Next Steps).
6. U.S. National Library of Medicine. (2006, January 12). PHENTERMINE.
7. National Capital Poison Center. (2019). Poison Control expert help online or by phone.