Inositol, a naturally occurring isomer of glucose, is a polyol precursor in a second messenger system important in some parts of the brain.  Research has been limited to small, short studies but with some promising results for depression, obsessive-compulsive disorder, and panic disorder.  Side-effects are minimal.  While inositol doesn't look like a powerful benefit, it might be worth trying in selected patients.  Inositol is available via the internet at reasonable costs if purchased as a powder.  Jarrow's 8 oz. (227 g) is available from iHerb.com for $12.  This would be $19 per month at 12 g/day for depression or $30 per month for 18 g/day for obsessive-compulsive disorders.

Since inositol is a naturally occurring substance, it cannot be patented and cannot be a prescription medication.  This, unfortunately, means that insurance won't pay for it and pharmaceutical companies won't be promoting it.

Side-effects have been reported as "minimal."  The total number of studies inositol for depression is four or five covering only 141-166 patients.  It's simply too early to draw any conclusions.  However, since it is relatively inexpensive with few side-effects, it appears acceptable as an add-on strategy.

Inositol Helped Depression, OCD, Panic: In DB PC studies, Israeli researchers found no benefit for schizophrenia, Alzheimer's, ADHD, or autism but did find benefit for 12 g/day for 4 weeks for 28 depressed patients, for 12 g/day for 21 panic patients, and 18 g/day for 13 OCD patients. Minimal side-effect. Levine, Ben Gurion U, Eur Neuropharm ’97;7:147. and Benjamen J, Agam G, Levine J, et al. Inositol treatment in psychiatry. Psychopharmacol Bull. 1995;31:167–175. Inositol, a naturally occurring isomer of glucose, is precursor for secondary messenger for some serotonin, noradrenergic, and muscarinic cholinergic receptors. Lithium might treat mania by reducing inositol levels. Oral inositol reduces some of the side-effects of lithium in man and behavioral effects in animals. The degree of anti-depressant effect in four weeks is said to be similar to imipramine. Psychopharm Bull ’95;31:167. An OCD study in Am J Psychiatry 9/96 notes the benefit of inositol was similar to the SSRIs, which is very good. It was of no benefit when given for 5 days at 6 g/d after ECT.  A panic study was in Am J Psychiatry 7/95 and depression Am J Psychiatry 5/95. Inositol also helps premees with respiratory distress syndrome. NEJM 5/7/92 and two other studies. Researchers found no benefit for diabetic peripheral neuropathy or retinopathy.  J Nutr ’95;125:725S

Adding Inositol to SSRI no Benefit: In a 4-week DB PC study of 27 depressed patients on an SSRI or SSRI + inositol found no difference. However, a similar lack of benefit adding lithium to TCA or MAOI + TCA, while other researchers have reported benefits from these combinations. Levine, Ben Gurion, Biol Psych 2/99;45:270

Adding Inositol No Benefit for Depression in DB: In a double-blind study of 42 people with severe depression who were not responding to standard antidepressant treatment, researchers found no improvement when inositol was added. Nemets B, Mishory A, Levine J, et al. Inositol addition does not improve depression in SSRI treatment failures. J Neural Transm. 1999;106:795–798

Inositol Helped Bipolar Depressed in Small DB: 25 patients in a DB PC study of 12 g/d for 6 weeks in which patients continued on mood stabilizers found 67% of twelve inositol-treated subjects had a 50% or greater decrease in the baseline MADRS scores compared to four (33%) of twelve subjects assigned to placebo (p = 0.10). Inositol was well tolerated with minimal side effects. Inositol as an add-on treatment for bipolar depression. Chengappa KN, Levine J, Gershon S, Mallinger AG, Hardan A, Vagnucci A, Pollock B, Luther J, Buttenfield J, Verfaille S, Kupfer DJ. Bipolar Disord 2000 Mar;2(1):47-55

Inositol May Have Helped Trichotillomania, Skin Picking, OCD: 3 cases, one as adjunct for SSRI. The other two refused to take an SSRI. Each was given 6 g three times a day. Improvement occurred at 4-8 weeks and all were much improved. J Clin Psychiatry 01;672:60; 

Inositol Background: Myo-Inositol (mI) is a key metabolic precursor to the phospoinositide (PI) metabolic pathway as a key component of central G-protein coupled receptor signaling systems, including several subtypes of adrenergic, cholinergic, serotonergic and metabotropic glutamatergic receptors. Results suggest that mI reduces 5HT2A-R function at the receptor-G protein level. While fluoxetine also reduced 5HT2A-R function, but to a lesser degree, imipramine increased 5HT2A-R function, which may explain why mI seems to be effective exclusively in selective serotonin reuptake inhibitor-sensitive disorders. In addition mI, and at high concentrations fluoxetine and imipramine, also reduces mAChR function. Furthermore the results suggest that the attenuating effect of mI on mAChRs is partially dependent on the PI metabolic pathway. Effects of myo-inositol versus fluoxetine and imipramine pretreatments on serotonin 5HT2A and muscarinic acetylcholine receptors in human neuroblastoma cells. Brink CB, Viljoen SL, de Kock SE, Stein DJ, Harvey BH. Potchefstroom, South Africa. Metab Brain Dis. 2004 Jun;19(1-2):51-70

Inositol's Benefit for Depression Not Clear: Reviewers found four trials using inositol for depression with a total of 141 participants. These were short term trials of double-blind design. The authors conclude that the trials did not show clear evidence of a therapeutic benefit, nor any evidence of poor acceptability. Ongoing studies should reduce this uncertainty. Inositol for depressive disorders. Taylor MJ, Wilder H, Bhagwagar Z, Geddes J. University of Oxford. Cochrane Database Syst Rev. 2004;(2):CD004049

Inositol Didn't Help PMS in Very Small Study: Inositol, a simple isomer of glucose, serves as a precursor in the phosphatidyl-inositol (PI) second messenger cycle. In a very small 6-month, 11-woman DB PC crossover study of PMDD, myo-inositol, 12 g daily, during the luteal phase only (14 days prior to menses) showed no beneficial effect for inositol over placebo. Myo-inositol has no beneficial effect on premenstrual dysphoric disorder. Nemets B, Talesnick B, Belmaker RH, Levine J., Ben Gurion University of the Negev, Israel. World J Biol Psychiatry. 2002 Jul;3(3):147-9

OCD: Reported Benefit: Inositol, a glucose isomer and second messenger precursor, regulates numerous cellular functions. Fourteen OCD subjects underwent single photon emission computed tomography (SPECT) before and after 12 weeks of treatment with inositol. There was 1) deactivation in OCD responders relative to nonresponders following treatment with inositol in the left superior temporal gyrus, middle frontal gyrus and precuneus, and the right paramedian post-central gyrus; 2) no significant regions of deactivation for the group as a whole posttreatment; and 3) a single cluster of higher perfusion in the left medial prefrontal region in responders compared to nonresponders at baseline. Significant reductions in the YBOCS and CGI-severity scores followed treatment. These data are only partly consistent with previous functional imaging work on OCD. They may support the idea that inositol effects a clinical response through alternate neuronal circuitry to the SSRIs and may complement animal work proposing an overlapping but distinct mechanism of action. Single photon emission computed tomography (SPECT) in obsessive-compulsive disorder before and after treatment with inositol. Carey PD, et al. University of Stellenbosch, Cape Town, South Africa. . Metab Brain Dis 2004 Jun;19(1-2):125-34.

OCD: In 19 OCD patients before and after 8 weeks of SRI treatment vs. 19 sex-matched and age-matched controls, before treatment, OCD patients had higher platelet IP3 content and fewer 5-HTT binding sites than the controls. Treatment with SRIs further lowered the number of 5-HTT binding sites, normalized platelet IP3 contents, and lowered the number of platelet 5-HT2A binding sites and whole-blood 5-HT concentrations below control values. The patients who improved most following SRI treatment had higher whole-blood 5-HT concentrations before treatment. OCD may involve the overstimulation of the phosphoinositide signaling system. Platelet serotonergic predictors of clinical improvement in obsessive compulsive disorder. Delorme R, et al. Hopital Robert Debre, Paris, France. J Clin Psychopharm 2004 Feb;24(1):18-23.

OCD: No Value Combining with SSRI: In a 6-week DB PC crossover study of just 10 OCD patients being treated with SRI medications, 18 g inositol had no beneficial effect on OCD or Depression. Inositol versus placebo augmentation of serotonin reuptake inhibitors in the treatment of obsessive-compulsive disorder: a double-blind cross-over study. Fux M, et al. Ben Gurion University of the Negev, Beer-Sheva, Israel. Int J Neuropsychopharm 1999 Sep;2(3):193-195.

Double-blind, placebo-controlled studies have shown the efficacy of adding pindolol (7.5 mg/d), risperidone (2 mg/d) and olanzapine (5-10 mg/d). PanMinerva Med 2002 Jun;44(2):83-91.

Panic Disorder: Inositol Helped: In a DB crossover study Of 20 Panic Disorder adults, inositol up to 18 g/day reduced the number of panic attacks per week by 4.0 compared with a reduction of 2.4 with fluvoxamine 150 mg/d. (p = 0.049). Nausea and tiredness were more common with fluvoxamine (p = 0.02 and p = 0.01, respectively). Because inositol is a natural compound with few known side effects, it is attractive to patients who are ambivalent about taking psychiatric medication. Double-blind, controlled, crossover trial of inositol versus fluvoxamine for the treatment of panic disorder. Palatnik A, et al. Ben Gurion University of the Negev, Beer-Sheba, Israel. J Clin Psychopharm 2001 Jun;21(3):335-9.