Naltrexone is marketed as its hydrochloride salt, naltrexone hydrochloride, under the trade names Revia and Depade. A once-monthly extended-release injectable formulation is marketed under the trade name Vivitrol. VIVITROL is indicated for the treatment of alcohol dependence in patients who are able to abstain from alcohol in an outpatient setting prior to initiation of treatment with VIVITROL. VIVITROL is indicated for the prevention of relapse to opioid dependence, following opioid detoxification. Naltrexone is a pure opiate antagonist and has little or no agonist activity. The mechanism of action of naltrexone in alcoholism is not understood; however, involvement of the endogenous opioid system is suggested by preclinical data. Naltrexone is thought to act as a competitive antagonist at mc, κ, and δ receptors in the CNS, with the highest affinity for the μ receptor. Naltrexone competitively binds to such receptors and may block the effects of endogenous opioids. This leads to the antagonization of most of the subjective and objective effects of opiates, including respiratory depression, miosis, euphoria, and drug craving. The major metabolite of naltrexone, 6-β-naltrexol, is also an opiate antagonist and may contribute to the antagonistic activity of the drug. Low dose naltrexone is an “off label” use of naltrexone. Normal naltrexone usage to break addictions is 50mg – 100mg. Usage of low dose naltrexone ranges in the area of 3 mg – 4.5 mg dosing and is prescribed in an oral pill form and is quite inexpensive. For people with multiple sclerosis, the dosage of LDN ranges from 1.5 to 4.5 ml per day.

Baclofen (brand names Kemstro, Lioresal, and Gablofen) is a derivative of gamma-aminobutyric acid (GABA). Baclofen is a muscle relaxer and an antispastic agent and is used to treat muscle symptoms caused by multiple sclerosis, including spasm, pain, and stiffness. It is primarily used to treat spasticity and is under investigation for the treatment of alcoholism. Although baclofen is an analog of the putative inhibitory neurotransmitter gamma-aminobutyric acid (GABA), there is no conclusive evidence that actions on GABA systems are involved in the production of its clinical effects. Baclofen is rapidly and extensively absorbed and eliminated. Absorption may be dose-dependent, being reduced with increasing doses. Baclofen is excreted primarily by the kidney in unchanged form and there is relatively large intersubjective variation in absorption and/or elimination. Baclofen is a direct agonist at GABA-B receptors. The precise mechanism of action of baclofen is not fully known. It is capable of inhibiting both monosynaptic and polysynaptic reflexes at the spinal level, possibly by hyperpolarization of afferent terminals, although actions at supraspinal sites may also occur and contribute to its clinical effect.

(S)-baclofen (or L-baclofen) is an enantiomer of baclofen, a direct GABA-B receptor mimetic. L-baclofen represents a significant improvement over racemic baclofen in the treatment of trigeminal neuralgia.

Arbaclofen (STX209, R-baclofen), a selective agonist of GABA-B receptors, has been investigated in clinical trials for the treatment of autism spectrum disorder ASD, phase II and for the treatment of patients with fragile X syndrome in phase III. As a result, the drug did not meet the primary outcome of improved social avoidance in FXS in either study. In spite of positive results in some children with ASD, further study will be needed to replicate and extend these initial findings. Arbaclofen has also been investigated in phase III clinical trials as a treatment for spasticity due to multiple sclerosis.