Generic name: Phentermine hydrochloride.

Other brand names: Adipex-P, Dapex, Fastin, lonamin, Obenix, Obephen, Obermine, Obestin-30, Parmine, Phentrol, Profast-SR, Tora, Unifast Unicelles, Wilpowr, Zantryl.

Fastin is a nonamphetamine appetite suppressant. It relieves hunger by altering nerve impulses to the appetite control center of the brain. 

Quick Facts About Fastin


Used for weight reduction on a short-term basis.

Fastin Dosage

Take after breakfast, not in the evening, lonamin capsules should be swallowed whole. Fastin should be used in conjunction with a behavior modification program. Avoid suddenly stopping Fastin after prolonged use; may cause depression or trouble sleeping.

  • Usual adult dose: Fastin — 1 capsule 2 hours after breakfast, lonamin — 1 capsule per day, taken before breakfast or 10 to 14 hours before bedtime.
  • Usual child dose: not generally prescribed for children under 12 years.
  • Missed dose: skip missed dose completely; return to schedule.

Fastin Side Effects

Overdose symptoms:

abdominal cramps, aggressiveness, confusion, diarrhea, exaggerated reflexes, hallucinations, high or low blood pressure, irregular heartbeat, nausea, panic states, rapid breathing, restlessness, tremors, vomiting. If you suspect an overdose, immediately seek medical attention. Fatigue and depression may appear after stimulant effects of Fastin. With fatal poisoning, convulsions and coma usually precede death.

More common side effects: changes in sex drive, constipation, diarrhea, dizziness, dry mouth, exaggerated feelings of depression or elation, headache, high blood pressure, hives, impotence, inability to fall or stay asleep, increased heart rate, overstimulation, restlessness, stomach or intestinal problems, throbbing heartbeat tremors, unpleasant taste.

No known less common or rare Fastin side effects.


Inform your doctor before combining Fastin with:

MAO inhibitors such as Nardil and Parnate, diabetes medications such as Insulin and Micronase, or high blood pressure medications such as Ismelin.

May intensify effects of alcohol; avoid use when taking Fastin.

Special Cautions

If pregnant or planning to become pregnant, inform f your doctor immediately. Not known if Fastin appears in breast milk.

No special precautions apply to seniors.

Not generally prescribed for children under 12 years.

  • Do not take if you have: hardening of the arteries, heart or blood vessel disease, overactive thyroid, glaucoma, or moderate to severe high blood pressure.
  • Should not take if you: are agitated, have abused drugs, or have taken mao inhibitors within the last 14 days.
  • If sensitive to or allergic to this or medications that stimulate the nervous system, should not take.
  • May impair your ability to operate machinery or perform potentially hazardous activities; use with extreme caution.
  • Monitor for psychological dependence; contact your doctor if you become dependent.
  • Overuse can cause: inability to fall or stay asleep, irritability, hyperactivity, personality changes, or severe skin disorders.
  • Use with caution if you have mildly high blood pressure.

Note: provides accurate and independent information prescription pills, over-the-counter medicines and natural products. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment. If you have questions about  dosage, or Fastin side effects, please contact your healthcare provider.