Phentermine (Ionamin)

1. Health Canada Product Monograph — Phentermine

• As a short-term (a few weeks) adjunct to caloric restriction, exercise, and behavioural modification in the management of obesity in patients with a BMI above the threshold defined in the product monograph.
• Authorized for short-term monotherapy only — not for use in combination with any other anti-obesity drug, including another noradrenergic agent or a GLP-1/GIP receptor agonist.
• The fixed-dose combination phentermine-topiramate (marketed as Qsymia in the United States) is not authorized for sale in Canada; do not assume it can be obtained or substituted locally.

Contraindicated in pregnancy. Confirm pregnancy status and discuss alternative therapy with the prescriber before dispensing.

• Contraindicated. Weight-loss pharmacotherapy of any kind is not recommended during pregnancy.

• Not recommended; avoid use while breastfeeding given the stimulant class and absence of adequate safety data in lactation.

• Use with particular caution given increased sensitivity to sympathomimetic cardiovascular effects (tachycardia, hypertension) in older adults, especially those with existing cardiovascular disease.

• Not established for pediatric use.

• 15-30 mg orally once daily, taken before breakfast or 10-14 hours before bedtime to reduce the risk of insomnia.
• Limit use to a few weeks only, consistent with the short-term authorization; do not use continuously as a long-term chronic-disease treatment the way GLP-1/GIP agents are used.
• Discontinue if tolerance develops (diminishing appetite-suppressant effect) rather than increasing the dose beyond the recommended range.

If overdose is suspected, seek emergency medical attention immediately or contact your regional Poison Control Centre without delay.

• Restlessness, tremor, hyperreflexia, tachypnea, confusion, hallucinations, panic, hypertension, tachycardia or bradycardia, cardiovascular collapse, and seizures have been reported with sympathomimetic amine overdose. Manage supportively; institute cardiac monitoring.

• Insomnia, dry mouth, restlessness, irritability, tremor, and headache.

Serious side effects require immediate discussion with the prescriber or emergency care.

• Pulmonary arterial hypertension and valvular heart disease have historically been associated with related appetite-suppressant combinations (notably fenfluramine/dexfenfluramine, both withdrawn); phentermine alone carries a lower but not zero cardiovascular signal — monitor blood pressure and heart rate.
• Dependence and withdrawal with prolonged or inappropriate use, given its amphetamine-related structure.

• Mild to moderate hypertension.
• History of anxiety or agitation, which sympathomimetic effects can worsen.

• Cardiovascular disease, including arrhythmia, coronary artery disease, and uncontrolled hypertension.
• Hyperthyroidism.
• Glaucoma.
• History of drug abuse.
• Agitated states.
• Concurrent or recent (within 14 days) monoamine oxidase inhibitor use — risk of hypertensive crisis.
• Pregnancy and breastfeeding.

• Monoamine oxidase inhibitors — contraindicated combination, hypertensive crisis risk.
• Other sympathomimetic amines or stimulants — additive cardiovascular stimulation.
• Alcohol — may potentiate central nervous system effects.
• Insulin or oral antidiabetic agents — caloric-intake changes during treatment may require dose adjustment of these agents.

• None specific beyond the general caloric-restriction context of use.

• Morning dosing, or at least 10-14 hours before bedtime, to reduce insomnia risk.

• Store at room temperature, protected from light and moisture, out of reach of children — this is a controlled substance and must be stored and tracked accordingly.

• This medication is authorized for short-term use only (a few weeks) — it is not intended as a long-term chronic-disease treatment the way newer GLP-1/GIP-based agents are.
• Do not combine with any other weight-loss medication.
• Take in the morning to avoid difficulty sleeping.