I would say using finasteride is potentially problematic. Inhibiting the enzyme in question will not just reduce DHT, but the production of many different neurosteroids, such as allopregnanolone which modulates GABA. This may be why finasteride users get insomnia, rage, anxiety etc.

Someone with a TBI is already struggling with at least some of these things most times. So I would advise against using this drug.

Allopregnanolone - Wikipedia

Allopregnanolone possesses a wide variety of effects, including, in no particular order, antidepressant, anxiolytic, stress-reducing, rewarding,[10] prosocial,[11] antiaggressive,[12] prosexual,[11] sedative, pro-sleep,[13] cognitive, memory-impairment, analgesic,[14] anesthetic, anticonvulsant, neuroprotective, and neurogenic effects.[4] Fluctuations in the levels of allopregnanolone and the other neurosteroids seem to play an important role in the pathophysiology of mood, anxiety, premenstrual syndrome, catamenial epilepsy, and various other neuropsychiatric conditions.