The goal of this clinical trial is to learn if drug SRX246 works to treat irritability, agitation, aggression and self-injury (IAAS) behaviors in adult males with Fragile X Syndrome (FXS). It will also learn about the safety of drug SRX246. The main questions it aims to answer are:

• Does drug SRX246 lower the number of times participants experience IAAS behaviors?
• What medical problems do participants have when taking drug SRX246? Researchers will compare drug SRX246 to a placebo (a look-alike substance that contains no drug) to see if drug SRX246 works to treat IAAS behaviors.

Participants will:

• Take drug SRX246 or a placebo every day for up to 8 months
• Have weekly checkups by phone or video to answer study questions
• Have periodically scheduled home visits by nurses to conduct medical check-ups and tests
• Keep a diary of their symptoms

Inclusion Criteria:

• Biological male, age 18 to 45 years inclusive
• Molecular genetic confirmation of the full Fragile X messenger ribonucleoprotein mutation (≥200 CGG repetitions)
• IAAS symptoms leading to a CGI-S score for Disruptive Behavior of 5 or more
• Reported history of aggression based on the CMAI-Agg subscale (average score >22) and an average associated disruptiveness scale of at least 3.
• IQ < 70
• Stable medication doses for the last month
• Has a caregiver who lives with or spends extensive time with the participant most days and can report behavioral symptoms
• Must be able to swallow study drug capsules whole

Exclusion Criteria:

• Medical condition contraindicating study participation
• SGPT and SGOT values 2 or more times the upper limit of normal
• History of psychosis
• Suicidal behavior