Phentermine Side Effects

Along with its desired effects, phentermine may cause unwanted side effects, some being symptoms of serious heart or lung problems.

Please consult your doctor immediately if you notice any of the following signs that you may be suffering from a serious adverse reaction to phentermine:

  • Chest pain
  • Trouble breathing
  • Fainting
  • Swelling of feet or lower legs
  • Difficulty in carrying out day to day activities

What are the common Side Effects?

There are other more common side effects, which may occur, but these do not usually require medical attention. They may be uncomfortable but should go away during treatment as your body adjusts to the medicine. However, if these side effects persist or become more problematic, you should contact your doctor for advice.

These are some of the most common phentermine side effects:

  • Change in sexual desire
  • Constipation
  • Diarrhea
  • Dizziness
  • Dry mouth (Xerostomia)
  • Headache
  • Insomnia
  • Mood changes
  • Nausea or vomiting
  • Rapid heartbeat
  • Stomach pain
  • Tiredness
  • Unpleasant taste

Here is a poll of the most common side effects experienced by our phentermine forum users:
phentermine forum side effects poll

As you can see in the chart, Xerostomia, or dry mouth, is by far the most common side effect, reported by over 73% of the respondents. Around half of respondents reported suffering from the side effect of insomnia, and many also report other reactions such as headaches, constipation, dizziness, and rapid heartbeat.

What are the Less Common Side Effects?

There are other side effects which are less common. Some of these are more serious than others, but you should contact your doctor if you become troubled by any of these:

  • Blurred vision
  • Clumsiness
  • Confusion
  • Depression
  • Drowsiness
  • Dysphoria (extreme anger, also known as 'phen rage')
  • Increased blood pressure
  • Irregular heartbeat or 'fluttering'
  • Irritability
  • Nervousness
  • Psychosis
  • Skin rash or itching

Other side effects not listed above may occur in some patients. If you notice any other side effects, please inform your doctor.

What are the Possible Phentermine Overdose Effects?

If you think that you may have taken a phentermine overdose then you should contact your doctor immediately. These side effects may indicate that you have taken an overdose of phentermine:

  • Confusion
  • Convulsions (seizures)
  • Dizziness
  • Fast Breathing
  • Fever
  • Hallucinations
  • Hostility with urge to attack
  • Irregular blood pressure
  • Irregular heartbeat
  • Lightheaded or Fainting
  • Depression, following a period of excitement
  • Tremors, Trembling, or Shaking
  • Overactive Reflexes
  • Panic
  • Restlessness
  • Severe nausea, vomiting or diarrhea
  • Stomach cramps
  • Tiredness or Weakness

If you are worried about the prospect of suffering with these side effects of phentermine, you might want to consider using an alternative to phentermine instead. officially recommends Phen Caps, an efficient weight loss supplement that will help you initiate your weight loss journey, while avoiding side effects such as those listed above.
If you want to learn more about Phen Caps, please click here.

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