As anyone that has taken biology in the upper years of high school knows "the mitochondria is the powerhouse of the cell" because it in this organelle (an "organ" of a cell) that all energy in the body is made; this is where the production of ATP (Adenosine Tri Phosphate) is made and in fact this is the currency of energy, all energy used comes from this.

The synthesis of ATP comes from a cyclical chemical reaction called "The citric acid cycle" or "Kreb's cycle", whereby about a dozen chemicals are used to form ATP. Nearly all of these chemicals are made by the body but three are not: citric acid, Ascorbic acid and nicotinic acid. These are not made in the body and we have to eat them, and it's easy to not get enough.

Krebs cycle converts glucose (a sugar) OR glycogen (a fat) into ATP but only in the presence of sufficient levels of citrate, ascotbic acid and Nicotinic acid. Citrate is abundent in diets in fresh leafy greens and cirus fruit (with lemons containing the most). Ascorbic acid is also known as Vitamin C, while Nicotinic acid is made from Niacin, (vitamin b3).

Citrate is not uncommon in diets, not many people don't have enough citrate. Ascorbic acid is less common, roughtly a third of people, according to Horrobin, are deficient in this. Niacin is the issue most of the time, individual needs vary and niacin is less common in todays modern diet than is used to be in the preindustrial era.

The brain uses more energy than any other organ and when energy needs are not met it does not work properly. Anxiety is the first symptom of this, in the long term this may turn into depression.

Luckily, simply taking niacin in some form, has a profound effect on mental health. But it's the one vitamin where a bit of care is needed. Niacin is a strong acid and can produce a stomach ache if taken an empty stomack, so always - no exception - take it after eating meal.

Niacin is available in three forms as a vitamin: Niacin, Niacinamide and "Non flushing Niacin". The pros and cons are discussed below.

Niacin
Pure Niacin is the cheapest and most effective. But it can (and usually) produced a "flushing" a red itchy rash that lasts an hour or two. It gets less each time, so the second time it's not as bad and after taking it a while it's barely noticeable if it even happens at all. This reaction is not harmful! It may seem scary but nobody has ever been harmed by this, and it will pass. Other side effect that may be experienced at the beginning of a Niacin regime are a slight shortness of breath and faintness. Niacin opens up all the capillaries which slightly lowers blood pressure. Flushing is common, the other side effects are rare and only occur in asthmatics. One positive side effect of niacin is it reduces the bad cholesterol and raises the good cholesterol and is the only substance known that does this. So, while the side effects can be annoying for the first day or two, many feel they're worth going through to gain the benefits of the cholesterol reduction.

Niacinamide
Niacinamide is the amide of Niacin and does not have the flushing side effects. Jon Prousky, the worlds foremost authoritu on anxiety issues, prefers this form pointing out that the flushing from pure Niacin is too scary. The downsides are it's more expensive than Niacin and does not lower cholesterol.

Non Flushing Niacin
Inositol hexaniacinate is a niacin containing compound that converts to Nicotinic acid in the body but bypasses the process that causes flushing. So, like niacin it does not cause flushing but also does not lower cholesterol. It tends to be a but more expensive than Niacinamide.

Dosage
How much to take varies. No two people have the same biochemistry and there is no standard dosage. One takes some and if that fixes ghe problem, great, if not, take more after a couple of weeks. This is repeated until a dosage is found that does cure the problem. The symptoms will stop once the right dosage is found. Note that the aounf to stop thye symptoms initially us generally more than a maintenance dose, and that once they've gone away the dosage can be lowered, week by week. When they come back step the dosage up a bit to keep them away.

Note that Niacin therapy was pioneered by Dr Abraham Hoffer in Regina Sask. when he was medical director at a hospital there. The seminal work on the subject was written by Pauling and Hoffer in 1967. Pauling was of course the two time Nobel prize winner that because of his discovery and explanation of the hydrogen bond in 1931 that founded the fields of biochemistry and molecular biology. Hoffer had success treating the anxiety that causes alcoholism and schitzophrenia with Niacin, and wrote 13 books on the subject. Since Hoffers death at 96 a few years ago, Jon Prousky, medical director of the Canadian College of Natural Medicine in Toronto is the leading authority of treating anxiety with niacin compounds.

References
[1] "Orthomolecular Psychiatry: Varying the concentrations of substances normally present in the human body may control mental disease."
https://www.science.org/doi/abs/10.1126/science.160.3825.265

[2] Niacinamide's potent role in alleviating anxiety with its benzodiazepine-like properties: A case report
https://www.researchgate.net/publication/268221528_Niacinamide's_potent_role_in_alleviating_anxiety_with_its_benzodiazepine-like_properties_A_case_report

[3] Supplemental Niacinamide Mitigates Anxiety Symptoms: Three Case Reports
https://www.researchgate.net/publication/242775707_Supplemental_Niacinamide_Mitigates_Anxiety_Symptoms_Three_Case_Reports

[4] Pharmacologic Use of Niacin https://journals.sagepub.com/doi/10.1177/2156587211399579

[5] Dr. Abram Hoffer worked to unlock secrets of the human brain
https://leaderpost.com/news/saskatchewan/dr-abram-hoffer-worked-to-unlock-secrets-of-the-human-brain

[6] The Psychedelic Pioneers
https://www.cultureunplugged.com/documentary/watch-online/play/50658/The-Psychedelic-Pioneers

[7] Margot Kidder And Abram Hoffer on mental illness
https://www.youtube.com/watch?v=lzKNmttAI2s