From all the videos I have watched where Dr. Hinz discusses how he got into using the Amino Acids, he does not reference it was from him having Bi-polar. He actually ran a weight-loss clinic in Duluth, Minnesota, which was/is one of the only cities in america where health insurance covers weight-loss treatment. So back in the mid 1990's his main focus was on treating patients looking to lose weight. The focus his clinic had was on using different drugs at the time to manipulate the patients appetite so that they would not crave food and thus be able to lose weight. During this time the main drug combination that was used were Fenfluramine/phentermine otherwise known as Fen-Phen. Within a few years of its main stream use, there were multiple studies showing up that showed there were side effects that affected the heart(I think, I don't remember for sure what the side effects were), so it got pulled of the market.

With this happening, Dr. Hinz now had no way to be able to curb his patients appetite, which meant he could not do anything for patients looking to lose weight. He then talks about how he read some literature about how some physicians were having success at curbing appetite using SSRI and SNRI drugs. So he transitioned to using those to see if he could get a similar result. With doing so, he found that none of his patients were getting the results that the physicians he read about were getting. So he called the physicians who wrote the medical report up, and realized that all of the patients who were being treated by those physicians had never taken Fen-phen, whereas every single patient he was treating had taken it. So he reasoned that in some way Fen-phen had affected patients to render SSRI's and SNRI's useless.

Since he understood that Fen-phen functioned in a way that resulted in depletion of monamines, he theorized that this depletion is what rendered the SSRI and SNRI drugs worthless since there would not be enough monamines for the drugs to work with in the system since they would already be depleted. So because of this, he then started working with amino acids, initially it just being 5-htp and L-tyrosine. They started databasing the results from using these substances and overtime they started to see patterns in patient responses, the way urinary levels of monoamines respond to changes in dosage, and defined what urinary levels optimize and eliminate symptoms for different disease types.

Sulfur amino acids, 5-htp, L-tyrosine, L-dopa, and L-trytophan all function together in one system with each having an effect on the other. For instance if you just take a sulfur amino acid like cysteine without taking a dopamine and serotonin precursor like L-tyrosine and 5-htp then you will cause dopamine and serotonin depletion. See here: Neurotransmitter depletion | AMA Certified Category 1 CME Relative Nutritional Deficiency Conference. For each patient and whether they need to continue to take the amino acids or not depends on the etiology of the condition. If the cause of the disease is post synaptic neuron damage, then to have continued symptomatic alleviation you have to take the amino acids for life. Your brain functions in bundles with different areas controlling different functions. If your substantia nigra is the origin of damage then you get symptoms of parkinsons disease, if the area controlling mood/affect is damaged then you get symptoms of depression, etc etc etc.

But lets say that the cause of the disease is depletion of the neurotransmitters, whether it be from taking a reuptake inhibitor, a poor diet, or taking any of the amino acids in improper balance with the others. In this case once you properly restored the needed chemicals to the necessary levels, you could then quit taking them and still achieve symptomatic relief since the depletion has been addressed. The third etiology of symptoms is from genetic anomalies. These are usually similar to the damage patient, with symptomatic relief only being maintained with continued amino acid intake.

Also, if a patient has Bi-polar and is treated, then yes they do take both amino acids and a mood stabilizing drug like Lithium. The way to identify these patients is that if they do not achieve relief of depressive symptoms when put in the phase 3 therapeutic ranges for serotonin and dopamine, then they are identified as being bi-polar. Here is an excerpt from the study they did on differentiating depression from bi-polar:

"This study contained 1600 patients who were diagnosed with recurrent major depression under the DSM-IV criteria. All patients had no medical history of mania or hypomania. All patients experienced no relief of depression symptoms on level 3 amino acid dosing values of the amino acid precursor dosing protocol. Of 1600 patients studied, 117 (7.3%) nonresponder patients were identified who experienced no relief of depression symptoms when the serotonin and dopamine amino acid precursor dosing values were adjusted to establish urinary serotonin and urinary dopamine levels in the Phase III therapeutic ranges. All of the 117 nonresponders who achieved no relief of depression symptoms were continued on this amino acid dosing value, and a mood-stabilizing drug was started. At this point, complete relief of depression symptoms, under evaluation with DSM-IV criteria, was noted in 114 patients within 1–5 days. With further dose adjustment of the mood-stabilizing drug, the remaining three nonresponders achieved relief of depression symptoms."

Hope this helps!