What does the evidence show about Phentermine's effects?

Read Off Label rates the evidence for Phentermine as Strong and the benefit magnitude as med-high, producing an overall grade of B- (6.0/10). Oldest weight loss drug still on market (1959).

What safety findings are reported for Phentermine?

Phentermine has a med-high risk profile in the database. Med-High (cardiac risk, BP/HR, insomnia, addiction potential, pulmonary hypertension with old fen-phen combo) Legal status: Rx (Schedule IV).

What does the low Safety score for Phentermine represent?

The Safety score is 3.5/10. It records the substantial harms described for one or more use contexts; the Benefit score, indication, dose, route, duration, population, and legal status remain separate parts of the evidence profile.

Rankings / Metabolic Health

Phentermine

Metabolic Health · Sympathomimetic

Also known as: Adipex-P ·Lomaira

Tier B-

High-risk evidence profile

Reviewed by Read Off Label · Last reviewed Jul 11, 2026 · How we grade

controlled-substanceprescription

High-risk evidence profile

6 / 10

Tier B-

Ev 8 Bn 6.5 Sf 3.5

Bottom line

Read Off Label grades Phentermine as B- (6.0/10) based on strong evidence, med-high benefit magnitude, and a med-high-risk safety profile.

Its high-risk evidence profile reflects a Safety score of 3.5/10; reported benefits and harms can differ by indication, dose, route, duration, and population.

Oldest weight loss drug still on market (1959).

Studied, labeled, or reported-use context: 15-37. — Rx; not individualized guidance.

Citation correction in progress

1 PubMed link was found to be unrelated to this entry and removed from public output. The remaining sources are shown below, but this row's claims and score still need a full source-by-source revalidation.

What the evidence says

Oldest weight loss drug still on market (1959). Pulled from combination (fen-phen) after valvular heart disease reports in 1997. Modern use typically short-term and with cardiovascular monitoring.

Mechanism

Amphetamine-derivative; stimulates norepinephrine release in hypothalamus; appetite suppression via catecholaminergic signaling

Studied, labeled, or reported dose & route

15-37.5 mg PO daily morning; intended for short-term (12 week) use

This records doses and routes described in studies, approved labeling, clinical practice, or documented use. It is not individualized guidance and does not establish safety; context changes with indication, formulation, health history, monitoring, and other medicines.

Citations

A link means the source informed this entry; it does not mean every claim on the page comes from that source. If a citation looks wrong or you want a claim re-checked, send a correction.

Common questions

What does the evidence show about Phentermine's effects?: Read Off Label rates the evidence for Phentermine as Strong and the benefit magnitude as med-high, producing an overall grade of B- (6.0/10). Oldest weight loss drug still on market (1959).
What safety findings are reported for Phentermine?: Phentermine has a med-high risk profile in the database. Med-High (cardiac risk, BP/HR, insomnia, addiction potential, pulmonary hypertension with old fen-phen combo) Legal status: Rx (Schedule IV).
What does the low Safety score for Phentermine represent?: The Safety score is 3.5/10. It records the substantial harms described for one or more use contexts; the Benefit score, indication, dose, route, duration, population, and legal status remain separate parts of the evidence profile.
What doses or routes are reported for Phentermine?: 15-37.5 mg PO daily morning; intended for short-term (12 week) use This is context from studies, approved labeling, clinical practice, or documented use; it is not individualized guidance and does not establish safety.
How does Phentermine work?: Amphetamine-derivative; stimulates norepinephrine release in hypothalamus; appetite suppression via catecholaminergic signaling

This is an independent synthesis of published research by a non-clinician. Scores are opinions supported by citations, not prescriptions. See the full disclaimer and methodology for how this score was produced and what it does and doesn't mean.