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Phentermine Side Effects
Published on August 16, 2022 and last updated for accuracy on August 17, 2022
Taking a phentermine capsule orally for weight loss is only effective for a limited time, normally for a few weeks. People who are significantly overweight or obese with a body mass index of 30 or more or a BMI of 27 but has specific health risk factors can benefit from this medication. Diseases like hypertension, hyperlipidemia, and diabetes are examples of such dangers. Phentermine should be used in conjunction with a reduced-calorie diet, regular exercise, and other lifestyle adjustments to be as effective in shedding extra pounds.
How Does Phentermine Work?
Phentermine is classified as an anorexic drug. One definition of a drug class is a set of pharmaceuticals that share a common mechanism of action. The symptoms of these diseases are generally treated with the same medications. (1)
How exactly does phentermine help you shed pounds? Evidence suggests that phentermine helps people lose weight by stimulating the production of hormones in the brain that make them feel full faster. This could help you reduce your food intake, leading to a healthier weight. (1)
Possible Outcomes of Using Phentermine
Phentermine it may interfere with your ability to get to sleep. As a class IV drug, it also has a potential for physical and psychological dependence or drug abuse. It may bring about a variety of undesirable outcomes, if not used properly. (1)
More Frequent Adverse Reactions
Some of the more prevalent phentermine adverse effects include:
- A weird taste in your mouth
- Unwell stomach
- Dry mouth
If the side effects aren’t too severe, you might feel better in a few days to a couple of weeks. Talk to your doctor or pharmacist if they get worse or don’t go away. (1)
Adverse Effects That Can’t Be Ignored
If you experience severe adverse effects, contact your doctor immediately. If you are experiencing symptoms that you believe could be life-threatening, you should dial 911 immediately. (1) Some examples of severe adverse effects and associated symptoms are as follows:
- Pulmonary hypertension of unknown etiology (PPH). This is a form of hypertension that primarily impacts the pulmonary and aortic arteries. The following are examples of possible symptoms: discomfort in breathing, odd feeling in the heart (quick, fluttering heart rates), dizziness, cyanosis, and fatigue.
- Other effects are swollen legs, chest problems, feeling of lack of oxygen, either when doing physical work or resting, and fainting.
- Rapid heartbeat (irregular heartbeat) and symptoms of heart disease such as palpitations and a heart murmur (fast, fluttering heartbeat), hypertension (high blood pressure).
- You may also experience restlessness such as tremors (uncontrollable rhythmic movement in one part of your body);
- Insomnia (trouble sleeping), and;
- Impairment of erection in men (trouble getting or keeping an erection).
The phentermine in pill form may have negative interactions with other drugs, vitamins, and herbs you may be taking. An interaction occurs when one substance modifies another drug’s activity. That’s not good, as it can ruin the drug’s effectiveness. (1)
Your doctor should handle your prescription regimen with care to help prevent adverse reactions. Be honest with your doctor about any supplements, vitamins, or herbs you take. Talk to your healthcare provider or pharmacist to learn about the potential drug interactions when using this medication. (1)
Drugs That You Should Never Combine with Phentermine
There is evidence that combining phentermine with other medicines can have dangerous consequences. (2) Do not combine phentermine with these medications. Medication examples include:
- MAOIs include isocarboxazid, phenelzine, rasagiline, selegiline, and tranylcypromine. Taking phentermine while also beginning or discontinuing the use of an MAOI is not recommended for the first 14 days after either action. Combining these medications increases the risk of a hypertensive emergency (a dangerous increase in blood pressure). (2)
- Amphetamines, benzphetamines, dextroamphetamines, diethylpropion, and phendimetrazine are other weight loss medications. There is a possibility that the side effects of both medicines will increase if used simultaneously. Such conditions include arrhythmia and hypertensive crisis, where blood pressure suddenly skyrockets (a severely abnormal heart rhythm). (2)
- Antidepressants that block serotonin reuptake include the SSRIs citalopram, fluoxetine, escitalopram, fluvoxamine, nefazodone, sertraline, and paroxetine. Combining these medications increases the risk of a hypertensive emergency (a dangerous increase in blood pressure). (2)
Drug Interactions That Cause Side Effects
Combining phentermine with some drugs can increase the risk of adverse effects. Several medications fall within this category, including:
Oral medications and insulin for diabetes, include exenatide, glipizide, glimepiride, liraglutide linagliptin, metformin, nateglinide, pioglitazone, rosiglitazone repaglinide, saxagliptin. (2)
If you take both of these medications, you could experience a dangerous drop in blood sugar. Diabetic medication dose reduction is an option discussed with your doctor. Your blood sugar levels may also need constant attention. (2)
Caution for Those with Allergies
There is a risk of a severe allergic reaction when taking phentermine. (2) Some of the symptoms include:
- Difficulty breathing due to throat or tongue swelling
- If you experience any of these signs, you should seek immediate medical attention by calling 911 or visiting an emergency room.
If you have had an adverse reaction to this medication or phendimetrazine tartrate, you should not retake it. Doing it again can be fatal. (2)
When used with alcoholic beverages, phentermine can have more severe adverse effects. Among the potentially harmful reactions are lightheadedness, nervousness, excitability, headache, constipation, diarrhea, dry mouth, and inability to sleep. Alterations in sexual desire or ability are also possible. (3)
You should consult your physician on your alcohol consumption. With the possibility of adverse consequences, you may need closer monitoring. (3)
Cautionary Statements for Those with Specific Medical Problems
Primary pulmonary hypertension (PPH) sufferers in the past: Do not take phentermine. In some cases, phentermine can exacerbate PPH. (3)
People who have had cardiac difficulties should not take this medication. Stroke, abnormal heartbeat (arrhythmia), heart failure, coronary artery disease, valve disease, and uncontrolled hypertension are all examples of such conditions. (3)
Your doctor may order 15, 30, or 37.5 mg. Take it once daily and never exceed your prescription. If you forgot to take a pill and it’s almost time for the next dose, skip the missed dose.
When taken in large doses, phentermine has been linked to dangerously high blood pressure increases. This could increase your heart rate. It’s possible that the added strain on your heart will make your cardiac condition even worse. (3)
Tell your doctor if you have hyperthyroidism (an overactive thyroid) or a family history of the condition. Phentermine has been known to increase in thyroid function. As a result, this could increase your thyroid levels drastically. (3)
This medication has the potential to elevate intraocular pressure in glaucoma patients further. Doing this could potentially ruin your eyesight forever. If you suspect glaucoma, you should talk to your doctor. (3)
When used by patients with diabetes, this medicine can lead to weight loss and improved glucose control. Diabetic medication dose reductions are an option discussed with your doctor. (3)
People with a preexisting substance abuse disorder should know that this medicine may lead to addiction. Long-term use of this drug is not recommended. Do not hesitate to discuss past or current substance abuse with your doctor. (3)
This medication can potentially worsen agitation symptoms, including causing sleeplessness and anxiety. If you’re anxious or upset, you shouldn’t take phentermine. (3)
Advice for Other Groups
These considerations are especially important for pregnant women: Phentermine falls into pregnancy risk category X. (3) There are two ramifications of that:
- No pregnant woman should ever use a medicine in Category X.
- Women of reproductive age taking this medication should use effective birth control.
If you become pregnant while taking phentermine, you should immediately stop taking the drug and contact your doctor. (3)
Possible Withdrawal Symptoms
If you’re on phentermine for a long time, especially at high doses and you stop taking it too soon, you may experience a few side effects, more appropriately known as withdrawal symptoms.
These include headaches, vomiting, diarrhea, stomach pain, irritability, high blood pressure, insomnia, palpitations, and more.
Always follow doctor’s orders when tapering doses.
Reasons to See A Doctor and When to Do So
- If you aren’t losing weight despite regular exercise, a low-calorie diet, and this medication, you should talk to your doctor. Remember that the drug’s effectiveness may not be seen for a while. (3)
- In the interest of breastfeeding mothers: Effects on a nursing infant have not been established for phentermine, but there is some evidence that it is excreted into breast milk. If you plan on breastfeeding, discussing this with your doctor is essential. You might have to choose between discontinuing nursing and stopping this medicine. (3)
- As people get older, they may experience diminished kidney function. Due to this, drug metabolism may be slowed down. Therefore, more of the medicine enters the bloodstream and remains there for a more extended period. You’re more likely to experience unwanted side effects due to this. (3)
- Children: No research on this drug has been done on young patients. People under the age of 16 shouldn’t take it. (3)
Tips to Manage or Prevent Phentermine Side Effects
The above mentioned side effects are treated differently depending on the severity and timing of the reaction. Make sure to always consult a physician.
Here are a few tips to help manage or control phentermine side effects:
- Use the lowest possible dose. Follow your dosage schedule strictly. Never overdose!
- Increase water intake
- Avoid alcohol and caffeinated drinks
- Exercise regularly
- Report any unpleasant symptoms immediately!