Please assess the completion status of the following clinical trial:

Trial Title: Effects of Nicotine on Brain Opioid Receptors

Study Design Characteristics:
- Allocation: None
- Intervention Model: None
- Observational Model: CASE_CROSSOVER
- Primary Purpose: None
- Time Perspective: PROSPECTIVE
- Masking: None
- Phase: None
- Number of Arms: None

Eligibility Criteria:
Inclusion Criteria:~* Non-treatment seeking smokers of European ancestry~* Between 18 and 50 years old~* Smoking at least 10 cigarettes per day for at least the past 6 months~* Able to provide informed consent~* Fluent, English-speaking~* Weight ≤ 300 lbs.~Exclusion Criteria:~* Current enrollment or plans to enroll in a smoking cessation program, or use other smoking cessation medications in the next 2 months~* Provide a Carbon Monoxide reading of ≤10 ppm at Medical screening.~* History of substance abuse and/or currently receiving treatment for substance abuse (e.g., alcohol, opioids, cocaine, marijuana, or stimulants)~* Current alcohol consumption that exceeds 25 standard drinks/week~* Providing a breath alcohol concentration (BAC) reading of \> 0.01 at any session.~* Women who are pregnant, planning a pregnancy, or lactating; all female subjects shall undergo a urine pregnancy test at each session~* Women of child-bearing age must agree in writing to use an approved method of contraception~* History or current diagnosis of psychosis, major current depression or bipolar disorder, ADHD, schizophrenia, or any Axis 1 disorder as identified by the MINI~* Serious or unstable disease within the past 6 months (e.g., cancer \[except melanoma\], heart disease, HIV)~* History of epilepsy or a seizure disorder~* History or current diagnosis (last 6-months) of abnormal rhythms and/or tachycardia (\>100 beats/minute); history or current diagnosis of COPD, cardiovascular disease (stroke, angina, coronary heart disease), heart attack in the last 6 months, uncontrolled hypertension (SBP\>150 or DBP\>90)~* Any medical or neurological condition that might interfere with the distribution of the radiotracer as determined by the study MD~* Current or past use (within past 12 months) of any medications containing naltrexone or other MOR antagonists (e.g., Revia, Trexan)~* Current use or recent discontinuation (within last 14-days) of the following medications~* Any form of smoking cessation medication (Zyban, Wellbutrin, Wellbutrin SR, Chantix, NRT)~* Recent (within last 2 weeks) or planned use of psychotropic medications (anti-psychotics, anti-depressants (tricyclic, SSRI, MAOI), anti-anxiety or panic medications, and stimulants (e.g., Provigil, Ritalin), and opiate-containing medications for chronic pain~* Allergic response to any form of opioids or naloxone~* Participants shall be instructed to refrain from using any study prohibited drugs (note - participants are allowed to take prescription medicines not in the exclusion list) throughout their participation in the study.~* Self-reported history of head trauma or prior seizure, brain (or CNS) tumor~* Self-reported history of claustrophobia (contraindicated for PET)~* Inability to complete the baseline study procedures within four hours and/or correctly, as determined by the principal investigator.

- Gender: ALL
- Minimum Age: 18 Years
- Maximum Age: 50 Years
- Healthy Volunteers: t

Study Arms:
- OPRM1 A118G AA genotype (Type: None): Individuals with the AA genotype at the OPRM1 A118G polymorphism.
- OPRM1 A118G AG or GG genotype (Type: None): Individuals with the \*/G allele at the OPRM1 A118G polymorphism

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

Answer: outcome: terminate
termination_type: lack of efficacy