I was thinking something similar, apparently 450mg/day is the max dose recommended for fibromyalgia, i was thinking of trying that and if it doesn't work then tapering off.
Need to make an appt with my doc to get the higher dose.
GABA doesn't cross the blood brain barrier. A few sources like to claim natural source can but both types being molecularly identical it makes no sense.
That said there are other ways to raise brain GABA, with some success.
The GABA is lozenge based, so it dissolves under the tongue so it passes efficiently, it worked within 30 minutes. Taking orally never worked.
Magnesium also helps to maintain GABA in the synapse along with other nutrients such as B6.