Phentermine vs. Alli

By consulting a doctor about weight loss aid, you will probably hear the names of these two effective and powerful medications used to treat obesity. These diet pills are recommended for those who failed to achieve the desired result by means of conservative weight loss methods.

Typically, such patients have obesity-related conditions, like heart problems, diabetes, uncontrolled blood pressure, high cholesterol, etc.

Both medications are created to help patients lose weight, despite the fact that each of them has its own excellent mechanism of action:

Phentermine reduces appetite by affecting hunger and satiety centers located in the central nervous system.

Alli reduces absorption of fats in the lumen of the gastrointestinal tract by an average of 30%.

Phentermine, as well as Alli, produces even better results if combined with other weight reducing programs, such as low-calorie diet, constant workouts and behavior changes. However, these drugs cannot be mixed with other weight loss supplements without doctor’s approval, as this can be dangerous for the overall health condition.

Phentermine features vs Alli Peculiarities

Phentermine is a powerful weight loss medication generally taken by patients with a big body mass and related health issues. This medication is prescribed to obese teens aged 16 years and older, as well as adults for a short term, up to three months.

Alli is an over-the-counter derivative of Orlistat. Despite the fact that one can buy Alli freely at pharmacy, it should be used only in adults older than 18 years. The duration of use makes 2 years.

The action of Phentermine is similar to amphetamine, as it also releases noradrenalin and dopamine in the brain, decreasing the appetite and suppressing hunger impulses. Additionally, this medication is effective, as it increases metabolism and leptin level in the brain, which signals about satiety.

The action of Alli is aimed at blocking the process of fats cleavage and absorption that enter the body together with human diet. Alli works only in the lumen of the gastrointestinal tract and does not affect the function of other internal organs. This drug is not absorbed into the systemic bloodstream, so it has fewer side effects.

Phentermine can be habit forming, producing severe side effects when stopped abruptly. Alli use can also be accompanied with side effects.

Common Phentermine side effects:

  • elevation of blood pressure;
  • insomnia, restlessness;
  • gastrointestinal disturbances.

Common Alli side effects:

  • oily spotting;
  • frequent urge to defecate;
  • abdominal pain / discomfort.

It should be considered that the prolonged use of Alli reduces absorption of fat-soluble vitamins A, D, E and beta-carotene. To make up for the deficiency of these vitamins, it is recommended to take a multivitamin supplement.

Despite all the advantages, Phentermine and Alli are not for anyone. These medicines are not recommended during pregnancy and breastfeeding. In addition, each of these drugs has its own contraindications.


  • glaucoma;
  • heart disease;
  • overactive thyroid;
  • uncontrolled hypertension.


  • cholestasis;
  • chronic malabsorption syndrome;
  • hypersensitivity to any component of this product.

While taking Phentermine, MAO inhibitors (Parnate, Nardil) are contraindicated. Combination of these drugs can lead to development of hypotonic crisis.

Alli cannot be taken by patients who had an organ transplant. Orlistat may reduce therapeutic efficacy of medicines used to prevent organ transplant rejection.

Do not take Phentermine or Alli without first consulting your doctor and do not share your drugs with others. Adhere to the doctor’s recommendations and the prescribed dosage regimen.

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