Side effects of Phentermine

Side effects of Phentermine

Phentermine is an active substance of many drugs for treatment of all types of obesity. The development of this substance was started in the last century and it was intended as a remedy for depressive states of people.

However, during the studies, scientists found out that Phentermine also had anorexigenic effect and thus provided a quick weight loss. Still, just as all the other weight loss drugs, tablets containing Phentermine can cause side effects.

  • Despite the fact that Phentermine doses are various (15 mg, 30 mg, 37.5 mg and 40 mg), it does not exclude side effects of Phentermine in people. Only the correctly adjusted Phentermine dose provides an effective anti-obesity therapy and reduces the risk of side effects.

Almost every age group of people (young, mature, elderly) faces the excess weight problem today.

  • The most common side effects of Phentermine in teenagers are nausea, nervousness and dizziness. Usually, these reactions do not last for long and disappear without complications quite fast.

Possibly, the reduction of therapeutic dose of Phentermine can lower the adverse reactions and patient will be able to continue his treatment course. It is another matter that side effects keep disturbing a patient for a longer time, affecting his quality of life.

Usually, Phentermine does not cause much discomfort during the treatment course.

However, an individual sensitivity to the active substance may cause serious side effects not only in children, but also in adults and elderly people.

  • People should immediately inform their doctor about such Phentermine side effects as quick weight loss, difficult breathing, chest pain, swelling of the face or extremities.

Most likely, the doctor will offer to reduce the daily dose, even despite a significant weight loss.

The most common Phentermine side effects in adults are high blood pressure, insomnia, tremor and headache. If a patient sticks to a prescribed dose of Phentermine, these symptoms should go away within the first week of using the drug.

When prescribing medications that contain Phentermine active ingredient to elderly people, a doctor should take into account the potential drug interactions. Because of obesity comorbidities, there is a need of using several drugs at a time (polypharmacy) as a rule.

Polypharmacy increases the likelihood of side effects of Phentermine in geriatric patients by several times.


Thus, to avoid the adverse effects during anti-obesity treatment, the doctor should avoid Phentermine drug interactions.

If it is possible, patients should avoid using Phentermine along with adrenomimetic drugs because Phentermine can block the therapeutic effect of adrenergic drugs.

  • During clinical studies, scientists found out that the most common side effects of Phentermine from the gastrointestinal tract could be manifested as unpleasant taste and dry mouth, diarrhea and constipation.

From the cardiovascular system, Phentermine can cause primary pulmonary hypertension, palpitations, tachycardia, high blood pressure and ischemic events.

Such body reactions to Phentermine are considered moderate side effects so they require a special attention of the doctor.

A concomitant use of alcohol and the drug can cause side effects of Phentermine that could have been avoided if a patient would refuse from soft drinks during anti-obesity therapy. Moreover, alcohol can increase or reduce the therapeutic effect of Phentermine.

For the conclusion, let us note that some factors may provoke side effects of Phentermine, these are:

  • Polypharmacy
  • Patient’s age
  • Individual Phentermine intolerance
  • High doses of Phentermine

Considering all these factors, we can reduce the likelihood of side effects of Phentermine or avoid them completely.