Inhability to recruit further participants due to SARS-CoV-2 pandemics.

The objective of this randomized clinical trial is to examine the efficacy of L-glutamine for the treatment of generalized anxiety disorder compared versus placebo.

Inclusion Criteria:

• Outpatients with generalized anxiety disorder defined by the criteria of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V)
• Generalized anxiety disorder is the primary psychiatric disorder.
• Untreated patients or; patients treated with paroxetine, sertraline, citalopram, escitalopram, venlafaxine or duloxetine at least for 6 weeks on a stable dose; or patients treated with any benzodiazepine at least for 4 weeks on a stable dose.
• Hamilton Anxiety Rating Scale score major or equal to 20 and a score major or equal to 2 on items 1 and 2 of the same scale at both screening and baseline.
• Clinical Global Impression-Severity major or equal to 4 at both screening and baseline.

Exclusion Criteria:

• Unable to give informed consent.
• Currently participating in another clinical research.
• Any other psychiatric disorder not included in the Anxiety Disorders section of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V). Secondary diagnosis of other anxiety disorders are allowed provided the diagnosis is not more prominent than generalized anxiety disorder symptoms.
• Suicide risk as assessed by the researcher at screening or baseline.
• History of substance abuse in the previous six months before the screening visit.
• Suffering a medically relevant or instable disease.
• If woman, being pregnant at screening visit.
• If woman, being breastfeeding.
• A score major or equal to 20 on the Montgomery-Asberg Depression Rating Scale at screening or baseline.
• As judged by a researcher, the patient might not adhere to the intervention or complete follow-up.
• History of use of a banned drug in the past two weeks prior the baseline visit; three weeks in the case of monoamine oxidase inhibitors; one week in the case of fluvoxamine or a tricyclic antidepressant; two weeks for any antipsychotic and; six weeks por long-acting injectable antipsychotics.
• History of use of L-glutamine the most part of the days of the previous month before the baseline visit.
• History of psychotherapy treatment in the past month before the baseline visit.