Phentermine and Surgery Guide: (dangers, risks, duration & benefits)

January 8, 2024 |

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Did you know that phentermine is the most prescribed anti-obesity drug in the US, with as many as 2.43 million prescriptions written in 2011?

Considering the case reports of interactions with anesthesia with phentermine use, millions of people could be at risk of encountering possible problems during surgery.

So, what could happen if you undergo surgery while taking phentermine?

The exact links between phentermine and the use of anesthesia during surgery aren’t known. However, there have been numerous accounts of patients experiencing serious complications, possibly due to phentermine use.

Because phentermine has an estimated half-life of 19-24 hours, researchers recommend taking the last dose at least 7 days before your scheduled surgery.

Take note, however, that you just can’t stop taking phentermine because abruptly doing so can lead to serious withdrawal symptoms, including cardiac arrest, tremors, and nerve damage.

So, what should you do before quitting phentermine before surgery? What are the dangers and risks of combining phentermine and surgery?

Are there safe diet pills for me to try?

Let’s discuss more on these topics to answer your questions below.

What are the Risks Associated With Phentermine and Surgery?

If you’re scheduled for surgery or any other medical procedure, always tell your medical team about any medication, drug, or dietary supplement that you’re taking.

These could save your life because certain drugs, such as phentermine, can put you in danger when combined with anesthesia and other medications used during surgery.

Doctors are likely to recommend putting a gap of at least 7 days between your last dose and your surgery schedule.

However, it can become tricky during emergency situations when you’ll need to get surgery as soon as possible. It’s not like you can wait for 7 days from your last dose before getting the surgery in such cases.

Acknowledging that some people might feel embarrassed about taking anti-obesity medication, researchers in a 2005 Anaesthesia Intensive Care journal study suggest direct questioning before any medical procedure.

They suggest arterial blood pressure monitoring, perioperative beta-blockade, and/or the use of clonidine to manage situations with phentermine patients during surgery.

So, why can’t you take phentermine before surgery?

Let’s dive into the exact reasons why this combination can be risky, even possibly deadly to some.

1. Interfering with the Anesthesia’s Effects

You’ll be administered anesthesia before surgery. It will prevent you from feeling pain during the procedure. If you’re given general anesthesia, then you’ll be asleep during the entire procedure.

As a stimulant, phentermine might interfere with the effects of anesthesia. That can be a complication because it leads to the possibility of feeling some pain during the procedure.

You might require a higher anesthesia dose, which can also lead to other complications.

2. Cardiac Risks

Studies indicate that anesthesia can sensitize the myocardium (the heart’s muscular tissues) to the effects of stimulants like phentermine and amphetamine.

If that happens, you can have a higher risk of a heart attack or cardiac arrest when your brain produces more neurotransmitters with phentermine use.

Some case studies also showed patients suffering from bradycardia (heart rate that’s too slow) due to phentermine use before surgery.

Such situations can be serious, possibly lead to surgical complications, and might even cause death.

3. Blood Pressure Problems

Surprisingly, case reports showed different effects of phentermine on the blood pressure of patients during surgery.

Several studies showed that it can increase blood pressure. That’s actually expected, considering that high blood pressure is among phentermine’s side effects.

However, there are also some case reports showing that phentermine can cause hypotension or dangerously low blood pressure during surgery.

Both cases can be dangerous.

High blood pressure can increase your risks of hemorrhage, stroke, heart failure, and a heart attack during and after surgery.

Low blood pressure can prevent oxygenated blood from reaching your organs, including your brain. It could increase your risk of shock, acute kidney injury, postoperative heart attack, and delirium.

Some studies even suggest that low blood pressure is a higher risk factor for death than high blood pressure before a surgical operation.

Phentermine & Wound Healing

Phentermine doesn’t appear to affect the rate of wound healing because its effects are more on the heart, brain, and nervous system.

Still, it’s important to inform your doctor about phentermine use to avoid the complications mentioned above.

Why Do You Have To Stop Phentermine use Before Surgery? Phentermine & Anesthesia Death

Any of the situations above can be dangerous to you during surgery and the postoperative stage. These can possibly lead to coma or death.

So, don’t feel shy or embarrassed to tell your doctor about taking phentermine before surgery. That tidbit of information can save your life.

How Long Do You Need To Be Off Phentermine Before Surgery

In the medical community, it is acknowledged that it would take around 5 half-lives before a drug is considered to be completely metabolized and eliminated from your body.

However, the number is not absolute and can be affected by several factors.

For example, phentermine is excreted faster in an acidic urinary pH ranging from 5.5 to 6.0. Studies show that as much as 84% of the dose could be excreted within just 24 hours in this pH range.

In contrast, only about 48% was excreted with an alkaline urinary pH ranging from 7.5 to 8.0 over the same period.

Considering that phentermine has a half-life of 19-24 hours (the time it takes for your body to metabolize 50% of the drug), you might say that it could take around 2.5 days (calculated as 5 half-lives x 12 hours) to remove it from your system.

But because it can be affected by several factors yet potentially deadly to have during surgery, doctors often recommend discontinuing phentermine use at least 7 days before the procedure.

However, some surgeons might recommend a longer period, with some only approving the surgery schedule if phentermine is discontinued for at least 2-3 weeks before the surgery date.

How To Safely Quit Phentermine Before Surgery

Important warning: Don’t get off phentermine without your doctor’s approval!

Phentermine is known to cause withdrawal symptoms, sometimes these can be serious.

It can vary but severe symptoms can include the following:

  • Memory loss
  • Tremors
  • Congestive heart failure
  • Nerve damage
  • Stroke
  • Seizures
  • Cardiac arrest (it can be deadly!)

But if you’re lucky, you might just experience these fairly common phentermine withdrawal symptoms:

  • Headaches
  • Lack of energy
  • Stomach pain
  • Vomiting
  • Diarrhea
  • Insomnia
  • Irritability
  • Heart palpitations
  • High blood pressure
  • Menstrual irregularities

So, how can you safely quit or temporarily stop using phentermine to get ready for surgery without experiencing these withdrawal symptoms?

The key is talking to your doctor.

You might not experience these symptoms if you’ve been using a low dose of phentermine for just a few days. But if you’ve been on a higher dose for a longer time, your doctor will likely reduce the dose gradually over the next few days.

However, because different people react to medications differently, it might take several weeks before you can safely quit using this anti-obesity drug.

Be sure to follow your doctor’s advice and try your best not to miss a dose. The faster you’re off the drug, the lower your risks during surgery.

Phentermine & Other Medical Procedures

Can You Take Phentermine Before A Colonoscopy?

No. Phentermine can interfere with the sedatives or anesthesia used before the procedure.

As a stimulant, phentermine can reduce the effects of anesthesia and sedatives. Although the effects won’t be as dangerous as other drug interactions, it’s still a good idea to quit phentermine use as directed by your physician.

Most doctors recommend colonoscopy procedures only after at least 7-14 days of the last phentermine dose.

However, these aren’t the only reasons why phentermine use should be stopped before a colonoscopy.

Phentermine can lead to the following:

  • Delay in gastric emptying
  • Ischemic colitis (a serious complication)

Let’s discuss these below.

Gastric Emptying & Colonoscopy

A colonoscopy requires a clear, empty colon. That’s why you won’t be allowed to eat anything solid at least a day before the procedure. You’re likely to be put on a clear liquid diet.

Some drugs like phentermine and fenfluramine can delay gastric emptying by as much as 15%. That means that food takes a much longer time to leave your stomach and is eliminated from your colon.

Although it won’t be dangerous and isn’t likely a cause for a medical concern, it can delay your colonoscopy schedule or invalidate your test results. You might have to take the test again.

That’s added hassle (and costs) to you.

Ischemic Colitis

This condition happens due to a restriction of blood flow to the colon. It can lead to bloody stools and abdominal pain.

Because phentermine use can lead to narrowing of your blood vessels and increased blood pressure, it could also increase your risks for ischemic colitis.

Studies show that this could be due to the release of vasoactive amines.

Although colonoscopy-induced ischemic colitis is rare, it’s best to avoid it from happening by temporarily stopping phentermine use.

Phentermine & Plastic Surgery

The dangers of phentermine and surgery don’t just stop with medical procedures but can also apply to plastic surgery.

Due to the possibility of serious complications with anesthesia, researchers recommend proceeding with caution before plastic and reconstructive surgeons decide to perform surgery on a patient using phentermine.

That’s especially true with elective surgery.

If the patient and doctor decide on proceeding with the surgery, the patient should be told of the risks.

Also, it’s important to get a skilled anesthesiologist to monitor intraoperative blood pressure and any signs of autonomic nervous system problems, including breathing and heartbeat issues.

Can You Take Diet Pills After A Tummy Tuck?

A tummy tuck is a cosmetic procedure wherein excess skin and fats are removed from your abdomen, and the reduced skin is draped over the repositioned tissues for a toned, smoother look.

Because a tummy tuck is actually a major surgery that requires weeks to heal, you’ll have to wait at least 2 weeks before taking any diet pills, supplements, or non-prescription medicine.

Phentermine and other diet pills can cause complications, including bleeding after the surgical procedure.

Your doctor might even recommend waiting longer, possibly 2-4 months after the procedure before you resume taking phentermine and other medications.

With phentermine causing so many complications and risks, you might want to consider trying other diet pills or drugs to lose weight.

Have you heard of PhenQ?

Let’s discuss this safer alternative to phentermine below.

Safer Weight-Loss Drug Recommendations

By taking safe weight-loss drugs like PhenQ, you get to enjoy its appetite suppression and energy-boosting effects without worrying about the side effects.

Its patented main ingredient a-LACYS RESET can boost your slimming efforts naturally, by encouraging your body to burn fats and increase your metabolism for more effective weight loss.

What we really love about PhenQ is that you don’t need to get a prescription to buy it, unlike phentermine. Plus, it works like phentermine in appetite suppression but also has other perks that can make it a safer, better choice.

Other advantages of using PhenQ include:

  • Rebalances metabolic disorders
  • Fights fatigue and boosts your energy
  • Improves muscle mass by focusing on burning fats and reducing protein catabolism which can burn muscles
  • Fights oxidative stress for increased anti-aging properties
  • Controls lactic acid build-up to reduce the burning sensation you feel during exercise

Still, if you’re scheduled for surgery, be sure to tell your doctor about taking PhenQ and other medications or supplements.

FAQs on Phentermine and Surgery

What Drugs Interfere With Anesthesia?

There are several drugs that could interfere with anesthesia. So, it’s best to stop taking them before surgery.

Monoamine Oxidase Inhibitors (MAOIs), including most anti-Parkinson drugs and antidepressants, can interfere with anesthesia. You might need to stop using them for at least 7-14 days before the surgery to ensure they’re completely out of your system.

Examples of MAOIs include the following:

  • Phenelzine (Nardil, Nardelzine)
  • Linezolid (Zuvox) (an antibiotic)
  • Tranylcypromine (Parnate, Sicoton)
  • Rasagiline (Azilect)
  • Selegiline (Eldepryl, Deprenyl)
  • Isocarbonazid (Marplan)
  • St. John’s Wort

Other drug interactions with anesthesia include these:

  • Bepridil
  • Cisapride
  • Dronedarone
  • Levoketoconazole
  • Mesoridazine
  • Pimozide
  • Piperaquine
  • Potassium
  • Potassium Citrate
  • Saquinavir
  • Sparfloxacin
  • Terfenadine
  • Tetracycline
  • Thioridazine
  • Ziprasidone

Can I Take Diet Pills Before Surgery?

No. Diet pills like phentermine can have chemical components that could interfere with the anesthesia and/or cause complications such as increased or lowered heart rate and blood pressure.

Is It Safe to Take Phentermine After Surgery?

Phentermine doesn’t interfere with wound healing but can increase your heart rate and blood pressure. This could lead to postoperative complications.

Wait for at least 6 weeks before resuming phentermine intake, and be sure to ask your doctor before doing it.

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