This study will investigate the effects of oxytocin on alcohol-related behaviors, social abilities, and physiological startle responses in healthy individuals and patients with posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD) using a randomized, placebo-controlled, dose-tiered, between-subject study design. Specifically, the investigators will determine if intranasal administration of a single dose of the pro-social neuropeptide oxytocin decreases alcohol-related approach bias and cravings, enhances social abilities, and decreases physiological hyperactivity. The investigators will also determine the optimal dose to achieve these effects and will explore psychosocial predictors of responses to oxytocin. The proposed work has the potential to yield a novel pharmacological treatment for AUD and PTSD, both leading causes of disability in the US Military for which currently available treatments are inadequate.

Inclusion Criteria:

1. Ages 18 to 75 (inclusive)
2. Current DSM-V diagnosis of PTSD
3. Current (past month) DSM-V diagnosis of a moderate to severe Alcohol Use Disorder

Exclusion Criteria:

1. Current or lifetime psychotic disorders, such as schizophrenia or bipolar disorder
2. Dementia or other neuropsychiatric disorders involving cognitive deficits or active symptoms impairing their ability to complete study tasks.
3. Subjects known to have clinically significant unstable medical conditions, including but not limited to clinically significant renal disease.
4. Use of disulfiram, naltrexone, or acamprosate for alcohol use disorder in the past week.
5. Needing acute medical detoxification from alcohol based on a score of 12 or more on the Clinical Institute Withdrawal Assessment of Alcohol Scale (CIWA-AD);
6. Subjects who are legally mandated to participate in an alcohol treatment program.
7. Subjects who have had a suicide attempt in the past 6 months or suicidal ideation in the 90 days prior to enrollment.
8. Subjects with seizure disorders that require anticonvulsant medications
9. Positive urine pregnancy test, women meeting DSM-V criteria for premenstrual dysphoric disorder or with diseases likely to influence hormonal or neuroendocrine status
10. Sensitivity to preservatives (in particular E 216, E 218 and chlorobutanol hemihydrate)
11. Nasal obstruction, discharge, or bleeding
12. Taking testosterone or estrogen/progesterone supplement, or 5HT1a agonists/antagonists, as these agents can alter oxytocin levels