As tyrosine is a precursor to both dopamine and noradrenalin, researchers have suggested that tyrosine depletion may play a role in the pathogenesis of depression. To date studies testing this hypothesis have produced mixed results. One study found that tyrosine- and phenylalanine-depleted individuals became less content and more apathetic than those given a balanced amino acid mixture (McLean et al 2004). However, a separate study in individuals with a past history of recurrent depression found that tyrosine depletion did not alter objective or subjective measures of mood (McTavish et al 2005), although plasma prolactin levels did increase and performance on a spatial recognition memory task was impaired (McTavish et al 2005).

Tyrosine appears to be most effective in treating depression associated with a lack Tyrosine 1173

of dopamine. One study involving patients with signs of dopamine-dependent

depression (DDD) found that treatment with oral tyrosine (3200 mg/day) caused an immediate improvement in mood, as judged by clinical impression and objective test scores (Montgomery-Asperg Depression Rating Scale) and sleep parameters from day 1 of treatment. Considered ineffective in other types of depression, supplementation with tyrosine should be limited to DDD (Mouret et al 1988a).

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