October 30, 2023

Top 9 phentermine Side Effects: What You Need to Know

phentermine side effects

Phentermine is a medication commonly prescribed to aid weight loss in individuals who are overweight or obese. Learn about phentermine side effects in this comprehensive guide. It is often used as part of a comprehensive treatment plan that includes a low-calorie diet and regular exercise. While phentermine can be effective in promoting weight loss, it is important to be aware of the potential side effects associated with its use. In this article, we will explore the most common side effects of phentermine and provide important information to help you make informed decisions about your healthcare journey.

Phentermine Side Effects

1. Dry Mouth

One of the most common side effects reported by individuals taking phentermine is dry mouth. This occurs because phentermine can decrease saliva production, resulting in a dry and uncomfortable sensation in the mouth. To alleviate this side effect, it is important to stay hydrated by drinking plenty of fluids throughout the day. Avoiding overly sweet or salty foods can also help minimize dry mouth. Additionally, over-the-counter dry mouth treatments such as gum, mouthwash, or lozenges may provide relief.

2. Insomnia

Another common side effect of phentermine is trouble sleeping or insomnia. Phentermine is a stimulant that can increase alertness and energy levels, making it difficult for some individuals to fall asleep or stay asleep. To mitigate this side effect, it is recommended to take phentermine in the morning or early in the day to allow the medication to wear off by bedtime. Practicing good sleep hygiene, such as avoiding caffeine and creating a relaxing sleep environment, can also help promote better sleep while taking phentermine.

3. Headache

Headaches are a potential side effect of phentermine due to its effects on blood vessels. Phentermine can cause changes in blood flow to the brain, resulting in the activation of pain signals and the onset of headaches. Staying hydrated and using over-the-counter pain relievers such as acetaminophen or ibuprofen may help alleviate headache symptoms. If headaches persist or worsen, it is important to consult your healthcare provider to determine the best course of action.

4. Tremor

In some cases, individuals taking phentermine may experience tremors or shaking. This side effect is usually mild and temporary, but it can be a sign that the dose of phentermine is too high. If tremors are accompanied by other symptoms such as fast breathing, confusion, or stomach cramps, it is important to seek medical attention immediately. It is crucial to take phentermine only as prescribed to avoid taking an excessive dose.

5. Changes in Behavior

Phentermine can affect brain chemistry and lead to changes in mood and behavior. Some individuals may experience a euphoric or "high" feeling, while others may experience restlessness or agitation. It is important to disclose any history of substance misuse or behavioral health conditions to your healthcare provider before starting phentermine. If you notice any significant changes in mood or behavior while taking phentermine, it is important to inform your healthcare provider for further evaluation.

6. Gastrointestinal Issues

Gastrointestinal issues such as constipation or diarrhea can occur as side effects of phentermine. These effects may be caused by the medication's impact on the digestive system. Staying hydrated and consuming a balanced diet rich in fiber can help alleviate constipation. Over-the-counter medications such as docusate sodium or polyethylene glycol may also provide relief. If gastrointestinal issues persist or worsen, it is advisable to consult your healthcare provider for further guidance.

7. Sexual Side Effects

Phentermine may have an impact on sexual function, leading to changes in libido or erectile dysfunction in some individuals. If these side effects become bothersome or persistent, it is important to discuss them with your healthcare provider. They can help evaluate the cause of these symptoms and provide guidance on managing them effectively.

8. Effects on the Heart

Phentermine can affect heart rate and blood pressure due to its stimulant properties. While some studies suggest that phentermine may lower blood pressure in individuals who take it for weight loss, it is important to monitor blood pressure regularly, especially in individuals with a history of heart problems. If you experience symptoms such as chest pain, rapid heartbeat, or shortness of breath while taking phentermine, it is essential to seek immediate medical attention.

9. Heart and Lung Disease

Individuals with pre-existing heart or lung conditions should exercise caution when considering phentermine. It is important to inform your healthcare provider of any history of cardiovascular conditions or lung disease before starting phentermine. They will evaluate whether the benefits of phentermine outweigh the potential risks in your specific case.

10. Contacting Your Healthcare Provider

If you experience any concerning side effects or have questions about your treatment with phentermine, it is crucial to reach out to your healthcare provider. They are the best resource for addressing your concerns and can provide personalized guidance based on your specific medical history and needs.


Phentermine is a medication commonly used to aid weight loss in individuals struggling with obesity. While it can be effective in promoting weight loss, it is important to be aware of the potential side effects associated with its use. Dry mouth, insomnia, headaches, tremors, changes in behavior, gastrointestinal issues, sexual side effects, effects on the heart, and heart and lung disease are among the potential side effects of phentermine. By being informed and proactive, you can work closely with your healthcare provider to manage these side effects and ensure a safe and effective treatment journey.

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