Tyrosine depletion appears to affect reward-based processing (McLean et al 2004) and tests involving reward/punishment processing are affected by dopamine depletion (Roiser et al 2005). A lack of D2 receptors and/or dopamine depletion states have been implicated in a number of conditions or destructive behaviours thought to be caused by poorly functioning biochemical reward systems.
Individuals tend to be at risk of multiple addictive, impulsive and compulsive behavioural problems, such as severe alcoholism, cocaine, heroin, marijuana and nicotine addiction, pathological gambling, sex addiction, chronic violence, posttraumatic stress disorder, risk taking behaviours and antisocial behaviour. As such, the use of tyrosine as a precursor to dopamine has a theoretical basis for use in this condition (Blum etal 2000).
Reward deficiency syndrome has also been proposed as a possible mechanism explaining the tendency to drug and alcohol addiction in schizophrenics (Green et al 1999).
To date, no large controlled studies are available to determine the clinical effects of tyrosine supplementation in this condition.
Drug withdrawal Tyrosine has been used to aid in the withdrawal of cocaine, caffeine and nicotine. Anecdotal reports suggest it is successful; however, large controlled studies are not available to determine clinical significance.
L-tyrosine supplementation has been considered because chronic cocaine use is believed to cause catecholamine depletion and cocaine withdrawal has been associated with major depression. To date, results from trials using tyrosine as a stand-alone treatment during cocaine withdrawal have produced disappointing results (Chadwick et al 1990, Galloway et al 1996). Although untested as yet, the effects of tyrosine may be of most assistance where a deficiency of dopamine D2 receptors is suspected, such as in reward deficiency syndrome.
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