Concussions are a common injury among athletes in the United States. The annual incidence of sports and recreational related traumatic brain injuries in the United States is 1.6 to 3.8 million, and the likelihood of an athlete in a contact sport experiencing a concussion is as high as 20 percent per season. Even mild traumatic brain injury, including concussion, can cause long-term cognitive problems that affect a person's ability to perform daily activities and to return to school or work. Far more concerning is the mounting body of evidence that concussions are not just transient injuries - but have cumulative effects. It has been well established in animal models that progesterone has neuroprotective benefits. Animal studies using progesterone for acute post-injury treatment have demonstrated reduced cerebral edema, reduced neuro-inflammatory markers, decreased neuronal loss, and improved behavioral outcomes. To date, there have been no studies to assess whether or not progesterone will be effective for the treatment of concussions. This double-blind placebo controlled trial will assess the ability of 5 days of oral micronized progesterone (Prometrium®) to shorten the duration of symptoms of an athlete diagnosed with concussion. The investigators hypothesize that athletes treated with progesterone will have faster resolution of their concussive symptoms. The investigators believe this study may be the first clinical trial to show an effective treatment for concussion.

Inclusion Criteria:

• Diagnosed with a concussion
• A 18 years or older
• Diagnosis < 24 hours from injury
• Consent obtained prior to concussion

Exclusion Criteria:

• Pregnant
• Active breast or reproductive organ cancers
• Allergy to peanuts
• History of or current thrombophlebitis or venous thromboembolic disorder
• Females taking birth control
• Known hypersensitivity or prior adverse reaction to progesterone
• Known liver disease