A concussion is a mild traumatic brain injury (TBI) that can occur from an impact to your head. Concussions are relatively common in contact sports like football, in falls, or as a result of vehicle collisions. The injury occurs following a sudden movement of your head and brain.

Concussions may cause several types of symptoms that begin immediately or hours to days later. Symptoms include headaches, brain fog or disorientation, and loss of consciousness.

However, research has not yet identified a connection between concussions and diarrhea.

There’s little to no research linking concussions with diarrhea, directly or indirectly.

Researchers of a 2018 study theorized that concussion may affect your autonomic nervous system (ANS), potentially leading to ANS dysfunction. Your autonomic nervous system controls basic functions like heart rate, body temperature, breathing rate, and digestion. ANS dysfunction happens when the nerves of the ANS are damaged.

ANS dysfunction may theoretically affect how quickly food is digested and how stool moves through your intestines, leading to side effects like diarrhea. But research is not definitive.

Other recent studies from 2018, 2021, and 2023 have noted a higher incidence of diarrhea in people receiving treatment for traumatic brain injuries, including those with serious concussions, in hospitals.

However, researchers of all three noted the higher incidence of diarrhea is likely linked to either antibiotic treatment or enteral nutrition in the hospital rather than the TBI itself. Enteral nutrition is a method of providing nutrition as a liquid formula through a tube.

Symptoms of a concussion vary based on the severity of the injury and the person injured. The Centers for Disease Control and Prevention (CDC) classifies symptoms by the following types:

Physical:

  • sensitivity to light or noise
  • dizziness or balance problems
  • fatigue or drowsiness
  • headaches
  • nausea or vomiting (soon after the injury)
  • vision problems, such as double vision or blurred vision

Cognitive:

  • concentration problems
  • short- or long-term memory problems
  • trouble thinking clearly
  • confusion

Emotional:

  • anxiety or nervousness
  • irritability
  • sadness

Sleep:

  • trouble falling asleep
  • irregular sleeping patterns (too much or too little)

It’s important that you see a doctor as soon as possible after experiencing any serious head injury, such as a vehicle crash or head collision in an athletic event. While most concussions resolve on their own, a doctor will determine the severity of the injury and whether additional treatment is needed.

Plus, concussions may be accompanied by other injuries to the head, back, or spine, which could be serious medical emergencies.

Medical professionals recommend immediate medical assistance if someone with a head injury has:

  • slurred speech
  • trouble waking up, or you can’t wake them
  • seizures
  • consistent vomiting
  • a history of multiple concussions