To determine the feasibility of whether the addition of key prebiotics administered orally can mitigate some of the most problematic side-effects of the most common psychiatric medications - weight gain and metabolic abnormalities caused by some antidepressants, mood stabilizers and antipsychotics. In the initial part of the study, we aim to determine feasibility of the study and evaluate participant compliance.

Our clinical trial will encourage the growth of Akkermansia muciniphila (AM) through enteric-coated orally-administered acetate (apple cider vinegar powder in capsules) in 16-to-28 year-old patients who have already experienced weight gain while on stable doses of psychiatric medication, with the hypothesis that the addition of this prebiotic will result in alterations in gut microbiota and measurable weight loss, as well as improvement in metabolic measurements.

Primary Objective:

• To evaluate feasibility of using acetate in a large-scale clinical trial, including considerations for protocol, study agent, recruitment, retention, adverse events, budget, staff, facility, and patient experience
• To estimate effect size of change in AM relative abundance by measuring pre- and post-intervention levels for use in designing future large-scale clinical trials

Secondary Objectives:

• To determine whether acetate administered orally shows an observable effect on weight gain as a side effect from antidepressants, mood stabilizers, and/or antipsychotics in a sample of participants already on stable doses of at least one of these medications
• To determine changes in metabolic syndrome profile, as indicated by blood pressure and high-density lipoprotein.
• To conduct preliminary analyses on any possible changes in mood/anxiety symptoms pre- versus post-intervention
• To identify and define other potential confounders or effect modifiers of our primary and secondary objectives that should be considered in future study designs

Inclusion Criteria:

For an eligible patient, all inclusion criteria must be answered "yes"

1. Signed informed consent obtained prior to any study-related activities
2. Patients of FEMAP who are between the ages of 16 and 28
3. Currently on a stable dose of an antidepressant, mood stabilizer, and/or antipsychotic drug AND have experienced what they deem to be problematic weight gain (approximately greater than 5% of initial body weight) that was temporally linked with initiating the drug, as confirmed by a psychiatrist
4. Have a body mass index of ≥ 21.7 kg/m2 (midpoint of normal BMI (18.5-24.9).

Exclusion Criteria:

1. Participants who are unable to follow multi-step instructions independently, as determined by the treating psychiatrist.
2. Participants who are pregnant or planning to get pregnant
3. Patients on medications that have weight loss as a potential side effect i.e. topiramate, metformin, psychostimulants.
4. Current active eating disorder i.e. bulimia nervosa, binge eating disorder, anorexia nervosa
5. Currently on a weight-loss diet plan i.e. ketogenic diet, detox diet
6. Currently using a medication for weight loss i.e. Contrave (bupropion / naltrexone), Saxenda (liraglutide)
7. Current use of dietary supplements for weight loss i.e. garcinia cambogia; or use within 4 weeks prior to study initiation
8. Bowel surgery
9. Crohn's disease or other bowel conditions
10. Blood/bleeding/liver/kidney disorders
11. Currently enrolled in other clinical trial which may affect their study outcome

We do not plan to share IPD with other researchers