Silymarin Treatment of Pathological Gambling: A Double-Blind, Placebo-Controlled Study

Gambling disorder is a significant public health problem that often results in a distinctive pattern of persistent and disabling psychological symptoms. Although once thought to be relatively uncommon, studies estimate that gambling disorder has a lifetime prevalence among adults of 1.6% and past-year prevalence of 1.1%. Patients with gambling disorder also experience significant social and occupational impairment as well as financial and legal difficulties.

Individuals with gambling disorder report chronically high levels of stress, and vulnerability to gambling addiction is enhanced by stressful events (4), particularly as stress may result cognitive problems leading to impulsive and unhealthy decisions. A stress response is elicited when sensations and Observations do not match existing or anticipated expectations. A primary endocrine response to stress is the secretion of glucocorticoids through the activation of the hypothalamic-pituitary-adrenal axis. Although their release serves to maintain homeostasis during acute episodes of stress, prolonged stress responses have been associated with structural brain damage both in humans and animals. In humans, stress also enhances addictive craving, and relapse to addiction is more likely to occur in individuals exposed to high levels of stress. Since oxidative stress may be implicated in the etiology of addictive behaviors, use of antioxidants to reduce relapse, improve cognitive functioning, and reduce addictive urges may be a sensible step.

Silymarin, a flavonoid and a member of the Asteraceae family, is extracted from the seeds of milk thistle (Silybum marianum) and is known to own antioxidative and anti-apoptotic properties. Silymarin has been reported to decrease lipid peroxidation. Furthermore, it has been demonstrated that its anti-oxidative activity is related to the scavenging of free radicals and activation of anti-oxidative defenses: increases in cellular glutathione content and superoxide dismutase activity. Milk thistle has been used for a range of psychiatric disorders including methamphetamine abuse and obsessive compulsive disorder, two psychiatric disorders with similarities to gambling disorder. The flavanoid complex silymarin in preclinical studies has been found to increase serotonin levels in the cortex, and ameliorate decreases in dopamine and serotonin in the prefrontal cortex and hippocampus associated with methamphetamine abuse. In the frontal cortex one of the functions of dopamine is to increase the signal to noise ratio, increased dopamine correlating with increased frontal performance. Studies have shown that the higher cortical dopamine levels are associated with improved frontal cortical cognitive performance. Cortical inhibition is felt to be the basis for top-down control of motivated behaviors. A recent randomized controlled study with milk thistle was conducted in Iran Thirty five participants with moderate OCD were randomly assigned to 200 mg of milk thistle leaf extract or 10 mg of fluoxetine three times daily for eight weeks. Results revealed no significant difference in treatment effects between milk thistle and fluoxetine from baseline to endpoint as both interventions provided a highly significant reduction in symptoms.

Silymarin or Milk Thistle may therefore offer promise for the treatment of individuals with gambling disorder. Pharmacological management of gambling symptoms has produced mixed results, with some studies showing a superiority of medication to placebo.

The current pilot study examines the tolerability and efficacy of milk thistle in the treatment of gambling disorder. We hypothesize that milk thistle will reduce the severity of gambling symptoms and improve patients' overall functioning.