This study will evaluate the efficacy and safety of ALT-801 once-weekly versus placebo as an adjunct to a reduced-calorie diet and increased physical activity in patients with obesity/overweight.

Inclusion Criteria:

• Written informed consent signed prior to entry into the study
• Male or female age 18 to 75 years, inclusive
• Body mass index (BMI) ≥ 30 kg/m2 or BMI ≥ 27 kg/m2 combined with at least one obesity-related comorbidity
• At least one unsuccessful weight loss attempt per investigator judgement
• Agreement to comply with the study-required life-style intervention and treatment during the full duration of the study
• Female subjects of childbearing potential who are not pregnant or breastfeeding, do not plan to become pregnant during the study, and agree to use effective birth control

Exclusion Criteria:

• Weight gain or loss > 5% in the 3 months prior to randomization or >10% in the 6 months prior to screening

• Diabetes and related conditions:

  1. History or clinical evidence of diabetes mellitus of any type, including Type 1, Type 2, or mature onset diabetes of the young (MODY)
  2. HbA1c > 6.5%, fasting glucose ≥ 126 mg/dL (6.9 mmol/L), and/or random glucose of ≥ 200 mg/dL (11.0mmol/L) at screening

• Obesity and related conditions:

  1. Obesity induced by known genetic causes or endocrine disorders (eg, Cushing Syndrome, inadequately treated hypothyroidism, defined as thyroid-stimulating hormone [TSH] > 6 mIU/L)
  2. History of bariatric surgery or other surgical treatment for obesity (eg, gastric banding, gastric bypass), or planned surgery or surgical treatment during the study. Liposuction and/or abdominoplasty performed >1 year before screening is allowed. Endoscopically placed intragastric balloons will be allowed if removed > 1 year before screening.

• Gastrointestinal conditions:

  1. History of acute or chronic pancreatitis within 1 year (365 days) before screening
  2. History of or acute significant gastrointestinal (GI) disorder (eg, peptic ulcers, severe gastroesophageal reflux disease [GERD],
  3. History of GI surgery, including cholecystectomy and antrectomy. Surgery for appendicitis and small bowel resection >20cm is acceptable.
  4. History of inflammatory bowel disease, celiac disease or any medical condition or surgery that could affect gastric emptying, stool frequency or stool consistency. (Irritable bowel syndrome is permitted provided that bowel frequency and consistency are normal off treatment.)

• Mental health conditions:

  1. Untreated depressive disorder, defined as a Patient Health Questionaire-9 (PHQ-9) score of ≥ 15 at screening
  2. Suicide ideation, defined as type 4 or 5 on the Columbia-Suicide Severity Rating Scale(C-SSRS) at screening, lifelong history of a suicide attempt, or suicidal behavior within 30 days before screening
  3. Other severe psychiatric disorder (eg, schizophrenia, bipolar disorder)