How a head injury can lower testosterone
Testosterone is made in the testes, but the order to make it comes from the brain. The hypothalamus signals the pituitary, a pea-sized gland at the base of the skull, and the pituitary releases LH and FSH to drive the testes. The same gland also controls cortisol, thyroid hormone and growth hormone.
The pituitary sits on a narrow stalk in a bony pocket, which makes it vulnerable when the head is struck or jolted. A 2015 review in Endocrine Reviews reports that the frequency of hypopituitarism after traumatic brain injury varies widely, from 15 to 50 percent of patients in most studies, falling to about 12 percent for persistent deficiency when testing is repeated. Growth hormone is the hormone most often lost, followed by ACTH (which drives cortisol), the gonadotropins LH and FSH, and TSH.
Car crashes are the most common cause of TBI, followed by falls, violence, sports injuries and blasts. The same review notes that pituitary dysfunction has also been described in boxers and kickboxers, which raises the question for anyone with repeated hits to the head, including football players, fighters and military veterans. The veterans page covers blast and service-related injuries.
Why the symptoms show up months later
The cruel part of post-injury hormone loss is how easily it blends in. MedlinePlus notes that hypopituitarism symptoms may develop slowly and vary greatly, listing fatigue, headache, low blood pressure, low blood sugar, weight loss and reduced sex drive. The 2005 consensus guidelines on screening after TBI point out that the signs of hypopituitarism often mimic the after-effects of brain injury itself, and that how severe the symptoms are does not necessarily match how severe the injury was.
So a man who had a concussion or a worse injury may notice, weeks or months later, that his energy never came back, his libido faded, his mood is flat and his workouts stall. Everyone, including him, puts it down to the injury or to depression. Sometimes that is right. Sometimes it is a pituitary that is no longer sending the signals it should.
Signs worth raising after any head injury include:
- Low libido or erectile problems that started after the injury.
- Fatigue that has not improved as other symptoms have.
- Loss of muscle or new weight gain around the middle.
- Feeling cold, constipated or slowed down.
- Dizziness when standing, salt cravings or unexplained weight loss.
The checks that point to pituitary involvement
A focused panel looks at each of the pituitary’s output lines:
| Test | What it shows after a head injury |
|---|---|
| Total testosterone, morning | Whether testosterone is truly low; repeated to confirm |
| LH and FSH | Low or “normal” values with low testosterone point to the pituitary, not the testes |
| Prolactin | Can be abnormal with pituitary stalk injury |
| Early-morning cortisol | Screens for low adrenal output, the most dangerous deficiency |
| TSH and free T4 | A low free T4 without a high TSH suggests a pituitary cause |
| IGF-1 | A marker of growth hormone activity |
The LH and FSH pattern is the key. The Endocrine Society guideline recommends measuring them to tell primary hypogonadism, where the testes fail, from secondary hypogonadism, where the brain or pituitary fails. After a head injury, the secondary pattern is the one to look for. Our pages on LH, FSH and secondary hypogonadism explain each piece.
Cortisol deserves special emphasis. MedlinePlus lists traumatic brain injury and pituitary problems among the causes of secondary adrenal insufficiency, a cortisol shortfall that can become dangerous during illness or stress. That is why a morning cortisol belongs on the same draw as testosterone, and why our morning cortisol test page matters here.
Why testosterone is not the first treatment
Low testosterone after a head injury is rarely the whole problem. If cortisol or thyroid hormone is also low, those deficiencies need to be identified and treated by an endocrinologist, and treating testosterone alone can leave a dangerous gap. A high prolactin, covered on our high prolactin in men page, needs its own workup and sometimes imaging.
Some early abnormalities recover on their own, which is why confirmed results matter more than a single draw soon after the injury. When testosterone remains low on repeat testing, with the rest of the pituitary assessed, testosterone therapy can become part of the plan, usually coordinated with the specialist managing the other hormones. The Endocrine Reviews authors note that hypopituitarism after TBI may slow functional recovery and cognition, which is a strong reason to look rather than wait.
Signs that need emergency care
Right after a head injury, some symptoms need emergency care immediately. MedlinePlus lists changes in alertness or consciousness, confusion that does not go away, seizures, weakness on one or both sides of the body, unequal pupils, repeated vomiting, and walking or balance problems. Call 911 for any of these.
Later on, call 911 or go to the ER for severe weakness with vomiting, abdominal pain, confusion or fainting, which can signal an adrenal crisis in someone whose cortisol is low.
How Ultimate Male approaches it
If you had a head injury and your energy, drive or libido never came back, tell the clinic about the injury when you call. The provider orders a morning panel that covers testosterone, LH, FSH, prolactin, cortisol and thyroid markers, and can add IGF-1 when growth hormone is in question, on site at San Gabriel or Downey with results in 24 to 48 hours. A PA-C or MD then walks through the results with you one-on-one.
Bring whatever records you have from the injury: emergency room or discharge notes, any head imaging reports, and a rough timeline of when each symptom started. Knowing whether low libido or fatigue began after the injury, rather than before it, is one of the most useful clues the provider has.
If the pattern points to the pituitary, you are referred to an endocrinologist for full pituitary testing and imaging before any testosterone decision, and our answer on pituitary MRI before TRT explains that step. Start with a free 10-minute call or see our preventative blood testing menu.
