My wife is 31 y/o uBPDw. When she was 14 she was hit by a car walking home from school. Since her accident she has had major aggression and mood disorders. Which I now know is BPD. I recently acquired her medical records and discovered something that was overlooked at the time of her accident. Her CT scan of her head showed premature calcification of the pineal gland. I had her start taking 5mg of melatonin at night before bed to see if it might help reduce the severity of symptoms. Wow her mood in the mornings started to improve.
Just wanted to share this in hopes it may help others.
If the pills are working for her...great. However, if the effects produce diminishing returns just keep in mind that isn't the melatonin itself that is the problem, but rather the delivery method. Melatonin is one of those supplements that suffers from piss poor bioavailability. The number one thing to pay attention to is sleep patterns. If the sleep patterns become intermittent that is a sign that the poor bioavailibility is at play and the short-half is causing intermittent or disrupted sleep.
I'd recommend at least keeping in the back of your mind trying out topical melatonin. For one, it will be better absorbed and for two it will produce a better overall effect since it will not enter the system all at once. The topical will produce more of an IV drip kind of effect.
If you need a reference so you know I am not blowing smoke up your

$$...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2909186/Wish you the best of luck regardless.
Cheers and best wishes!
-SC-