The purpose of this study is to see if the drug tecovirimat helps people with mpox (formally known as monkeypox) heal faster. The study will also help us understand more about how human mpox causes disease and how the body fights off infection. 
   
Tecovirimat is approved by the U.S. Food and Drug Administration (FDA) for the treatment of smallpox and has been given safely to some people with mpox in the recent outbreak. It is considered investigational in this study as it has not yet been approved to treat mpox.
   
Participants in this study will be randomized to receive either tecovirimat or placebo. Participants will also have physical exams, record their symptoms daily and complete questionnaires, provide blood and urine samples, and provide (or a study team member will obtain) swabs of the sores on their body.
   
Participants have the option of remote participation that does not include specimen collection. The total length of study participation is about two months.