Please assess the completion status of the following clinical trial:

Trial Title: Inhaled Nitrous Oxide for Treatment-Resistant Depression: Optimizing Dosing Strategies

Study Design Characteristics:
- Allocation: RANDOMIZED
- Intervention Model: CROSSOVER
- Observational Model: None
- Primary Purpose: TREATMENT
- Time Perspective: None
- Masking: DOUBLE
- Phase: PHASE2
- Number of Arms: 3.0

Eligibility Criteria:
Inclusion Criteria~1. Adults 18-75 years of age;~2. Current diagnosis of unipolar major depressive disorder (MDD) without psychosis as confirmed by structured clinical interview for DSM-IV disorders;~3. A score of \>= 9 on the Montgomery-Åsberg Depression Rating Scale (MADRS);~4. Documented (i.e., chart review) lifetime failure to respond to \>=3 adequate dose/duration antidepressant treatment trials, ≥1 medication failure in the current depressive episode;~5. Good command of the English language.~Exclusion Criteria~1. Meets criteria for any DSM-IV diagnosis for schizophrenia, bipolar, schizoaffective, obsessive-compulsive, personality, or panic disorders;~2. Any recent (within past 12 months) history of substance dependence or abuse (except tobacco), determined by reported history or urine drug screen;~3. Ability to become pregnant and not using effective contraception;~4. Contraindication against the use of nitrous oxide:~   1. Pneumothorax~  2. Bowel obstruction~  3. Middle ear occlusion~  4. Elevated intracranial pressure~  5. Chronic cobalamin and/or folate deficiency treated with folic acid or vitamin B12~  6. Pregnant patients~  7. Breastfeeding women~5. Inability to provide informed consent;~6. Any other factor that in the investigators' judgment may affect patient safety or compliance

- Gender: ALL
- Minimum Age: 18 Years
- Maximum Age: 75 Years
- Healthy Volunteers: f

Study Arms:
- 1. 25% nitrous oxide, 25% nitrogen, 25% oxygen (Type: EXPERIMENTAL): Participants will be studied for 14 visits over approximately 18 weeks. The participants will receive 1 hour-long gas inhalation mixtures at 3 different times, which are randomly assigned.
- 2. 50% nitrous oxide, 50% oxygen (Type: EXPERIMENTAL): Participants will be studied for 14 visits over approximately 18 weeks. The participants will receive 1 hour-long gas inhalation mixtures at 3 different times, which are randomly assigned.
- 3. Placebo gas: 50% nitrogen(inert), 50% oxygen (Type: PLACEBO_COMPARATOR): Participants will be studied for 14 visits over approximately 18 weeks. The participants will receive 1 hour-long gas inhalation mixtures at 3 different times, which are randomly assigned.

Based on this trial design, predict the completion outcome and termination type (if applicable).