Phentermine's Impact on Treatment in Teens (PhITT)

Phentermine's Impact on Treatment in Teens (PhITT): A Randomized Placebo-Controlled Trial of Phentermine for Adolescents With Obesity

PhITT is a Phase IIb, multicenter, randomized, double-blind, placebo-controlled clinical trial evaluating the efficacy and safety of phentermine (16 mg daily) in adolescents aged 12 to <18 years with obesity. Conducted across approximately 10 sites within the IDeA States Pediatric Clinical Trials Network (ISPCTN), the study aims to enroll up to 240 participants and then randomize up to 198 who meet eligibility criteria, randomized in a 2:1 ratio to phentermine or placebo over a 52-week treatment period, followed by a 2-week withdrawal assessment.

Study Overview

• Status: Not yet recruiting
• Conditions: Childhood Obesity
• Intervention / Treatment: Drug: Phentermine; Drug: Placebo

• Study Type: Interventional
• Enrollment (Estimated): 240
• Phase: Phase 2

Contacts and Locations

• Study Contact: Name: Aubrey VanStory; Phone Number: 402-559-4815; Email: aubrey.vanstory@unmc.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: No

Description

Inclusion criteria* include, but are not limited to:

• Age ≥ 12 years and < 18 years at time of consent;
• Tanner Staging ≥ 2 at the time of screening;
• Obesity (BMI ≥ 95th age- and sex-specific CDC percentile or BMI ≥ 30 kg/m2);
• Biological females must agree to use adequate contraception, defined as double barrier methods, stable hormonal contraception plus single barrier method, tubal ligation, or abstinence.

Exclusion criteria* include, but are not limited to:

• Contraindications to phentermine in adults such as:

  • A history of cardiovascular disease (e.g., coronary artery disease, stroke, clinically significant congenital heart disease, clinically significant cardiac arrhythmias, and congestive heart failure);
  • History of glaucoma;
  • Current or recent (within 14 days of screening) use of a monoamine oxidase (MAO) inhibitor;
  • Any previous history of drug dependency or current use of an illicit substance (positive urine drug screen);
  • Current pregnancy or breastfeeding;
  • Plans to become pregnant within the study duration;
  • Known hypersensitivity to sympathomimetic amines;
• Current nicotine use or nicotine cessation within 3 months of screening;
• Stage 2 hypertension (or greater) or taking any medication to treat hypertension;
• Current type 1 or type 2 diabetes mellitus or taking any medication to treat diabetes or prediabetes;
• Current or recent (within 3 months of screening) use of prescribed weight loss medication(s)/medically prescribed diets (e.g., low calorie, meal replacement/herbal agents/dietary supplements or weight loss program);
• Current or recent (within 3 months of screening) use of other sympathomimetic amines such as stimulants to treat attention- deficit/hyperactive disorder;
• Use of chronic systemic glucocorticoid therapy (consecutive use of 3 months or more) or other steroid hormone therapy other than oral contraceptives;
• Use of tricyclic antidepressants, lithium, levodopa, or dopamine receptor agonists;
• History of bariatric surgery;
• History or current diagnosis of schizophrenia, psychosis, bipolar disorder, or mental illness requiring hospitalization within 12 months of screening;
• History of suicide attempt within 2 years or self-harm within 3 months of screening;
• Current Patient Health Questionnaire-9 (PHQ-9) score of ≥ 10;
• Current suicidal ideation type 4 or 5 on Columbia Suicide Severity Rating Scale (C-SSRS);
• Current Eating Attitudes Test-26 (EAT-26) score ≥ 20 or any history of anorexia or bulimia.
• Current condition or disease interfering with metabolism, such as untreated hypo- or hyperthyroidism, Cushing's syndrome;
• Current clinically significant hepatic aspartate transaminase (AST) or alanine transaminase (ALT) > 3x upper limit of age- and sex-specific normal range or renal disease (creatinine clearance < 60 mL/minute); hypertriglyceridemia (triglyceride ≥ 400 mg/dL) or syndromic or monogenic obesity;
• Any clinically significant abnormalities on a standard 12-lead electrocardiogram at baseline;
• Heart rate > 100 bpm at screening;
• Current or recent use of any investigational medication or device or participation in an interventional clinical trial within 30 days of screening;
• Any clinically significant medical or psychiatric condition or laboratory abnormality that may increase the risk associated with trial participation, investigational product administration, or interpretation of trial results.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Phentermine 16 mg Group; Participants in this arm will receive phentermine 16 mg daily, administered as two 8 mg tablets taken orally once	Drug: Phentermine; Phentermine 16 mg administered orally once daily in the morning for 52 weeks. The dose is provided as two 8 mg tablets. Participants also receive lifestyle education handouts at each study visit. The intervention is designed to evaluate the efficacy and safety of phentermine for weight loss in adolescents with obesity.
Placebo Comparator: Placebo Group; Participants in this arm will receive placebo tablets that are visually identical to the phentermine tablets but contain no active pharmaceutical ingredient. The placebo will be taken orally once daily in the morning for 52 weeks. All participants will also receive lifestyle education handouts at each study visit. This arm serves as the control group for evaluating the efficacy and safety of phentermine in adolescents with obesity.	Drug: Placebo; Placebo tablets that are visually identical to phentermine tablets but contain no active pharmaceutical ingredient. Administered orally once daily in the morning for 52 weeks. Participants also receive lifestyle education handouts at each study visit. This control arm is used to evaluate the efficacy and safety of phentermine in adolescents with obesity.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Percent Change in BMI from Baseline at Week 52	Change in body mass index (BMI) expressed as a percentage of baseline BMI at week 52.	52 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Number of Treatment-Emergent Adverse Events (TEAEs)	Count of TEAEs deemed probably or definitely related to study drug, including common side effects	52 weeks
Number of Treatment-Emergent Adverse Events of Special Interest (TEAESIs)	Count of TEAESIs deemed probably or definitely related to study drug, including tachycardia, hypertension, depression, suicidality, and withdrawal symptoms	52 weeks

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Changes in Cardiometabolic Risk Factor Waist Circumference	Change in waist circumference from baseline	52 weeks
Changes in Cardiometabolic Risk Factor Blood Pressure	Change blood pressure from baseline	52 weeks
Changes in Cardiometabolic Risk Factor Glucose	Change in glucose from baseline	52 weeks
Changes in Cardiometabolic Risk Factor Lipids	Change in lipids from baseline	52 weeks
Changes in Cardiometabolic Risk Factor Hemoglobin A1C	Change in hemoglobin A1C from baseline	52 weeks

Collaborators and Investigators

• Sponsor: Russell McCulloh, MD
• Collaborators: National Institutes of Health (NIH); IDeA States Pediatric Clinical Trials Network
• Investigators: Study Director: Russell McCulloh, MD, UNMC

Study record dates

Study Major Dates

• Study Start (Estimated): December 1, 2025
• Primary Completion (Estimated): January 1, 2028
• Study Completion (Estimated): January 1, 2028

Study Registration Dates

• First Submitted: December 5, 2025
• First Submitted That Met QC Criteria: December 12, 2025
• First Posted (Actual): December 15, 2025

Study Record Updates

• Last Update Posted (Actual): December 15, 2025
• Last Update Submitted That Met QC Criteria: December 12, 2025
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: Adolescent Obesity; Weight Loss; Pediatric Obesity; Phentermine; BMI Reduction
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Body Weight Changes; Overweight; Obesity; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Weight Loss; Pediatric Obesity; Organic Chemicals; Amines; Phenethylamines; Ethylamines; Amphetamines; Phentermine
• Other Study ID Numbers: STUDY00161879; U24OD038400 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual-level data including baseline characteristics, outcome measures and adverse events.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ICF

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No