Inositol

Cellular Signaling: Inositol is a critical component of the phosphoinositide cycle, serving as a second messenger in intracellular signal transduction pathways. It facilitates communication within cells, influencing processes like hormone response and growth factor signaling (source).
Insulin Sensitization: It enhances insulin sensitivity, which is particularly beneficial for conditions like polycystic ovary syndrome (PCOS) and metabolic syndrome. Studies suggest it improves insulin action, potentially reducing blood glucose levels and aiding in conditions associated with insulin resistance (source).
Neurotransmitter Modulation: Inositol influences neurotransmitter synthesis, notably serotonin, which impacts mood and mental health. It has been explored for treating depression, anxiety, and obsessive-compulsive disorder (OCD), with evidence suggesting it modulates neurotransmitter activity in the brain (source).
Osmoregulation: In the brain, Inositol acts as an osmolyte, helping maintain cell volume and fluid balance, which is crucial for neurological function. Its concentration is notably high in brain tissue, supporting osmoregulation (source).
Structural Role: As phosphatidylinositol, it is a structural component of cell membranes, contributing to membrane integrity and function (source).

The onset of clinical effects for these actions varies, with research indicating that therapeutic benefits, particularly for mental health and metabolic conditions, are typically observed within 2-4 weeks (source). This timeline aligns with the need for sustained supplementation to achieve significant physiological changes, especially for chronic conditions.
Pharmacokinetics

Half-Life: Studies in preterm infants report a half-life of approximately 5-8 hours, with specific values ranging from 5.22 hours to 7.90 hours (source).
Bioavailability: Inositol is absorbed from the small intestine, with oral ingestion leading to peak plasma concentrations around 4 hours post-dose, indicating good oral bioavailability (source).

Therapeutic Doses: For mental health conditions like depression and anxiety, doses typically range from 12-18 g/day, often taken in divided doses (source).
Safe Range and Side Effects: Inositol is generally considered safe up to 18 g/day, with side effects like nausea, diarrhea, and gas reported at doses above 12 g/day (source).
Minimum Effective Dose: This varies by condition, with research suggesting 1-2 g/day as effective for some metabolic benefits, while higher doses are needed for mental health, starting at 12 g/day (source).
Maximum Safe Dose: Not explicitly defined, but studies using doses up to 18 g/day for extended periods (e.g., 3 months) report no significant adverse effects, indicating a high safety margin (source).
LD50 and Toxicity: In rats, the LD50 is reported as 10 g/kg body weight orally, indicating very low toxicity (source). For a 70 kg human, this translates to 700 g, far exceeding typical therapeutic doses, suggesting minimal risk of toxicity at recommended levels.
Dangerous Doses: Given the high LD50 and lack of reported serious toxicity, dangerous levels likely exceed 18 g/day, but specific thresholds are not established. Side effects at higher doses are mild, suggesting a wide therapeutic window, though caution is advised above 18 g/day due to potential mineral absorption issues at very high doses (source).

Condition	Therapeutic Dose (g/day)	Minimum Effective Dose (g/day)	Notes
Mental Health (e.g., Depression, Anxiety)	12-18	12	Effects seen in 2-4 weeks
PCOS and Metabolic Syndrome	2-4	1-2	Often combined with folic acid
Gestational Diabetes	4 (2 g twice daily with folic acid)	2	Prevents onset, used during pregnancy