Although a modest statistically significant benefit of pramipexole over placebo was detected, neither the response rates (40% compared with 33%) nor the remission rates (27% compared with 23%) differed significantly between groups. Dosages were modest (mean=1.35 mg/day; maximum=2.0 mg/day) ... To our knowledge, this is the first case series of adjunctive pramipexole in patients with treatment-resistant depression for whom at least four previous treatments in the current episode had failed. Overall, 76% of the patients showed a meaningful clinical response that persisted, while 24% were intolerant or nonresponsive to pramipexole. Effective pramipexole dosages ranged from 0.75 to 5.0 mg/day. The mean effective dosage of pramipexole in responders and remitters (N=32) was 2.46 mg/day". Side effects
Common side effects of pramipexole may include:
Headache
Peripheral edema
Hyperalgesia (body aches and pains)
Nausea and vomiting
Sedation and somnolence
Decreased appetite and subsequent weight loss
Orthostatic hypotension (resulting in dizziness, lightheadedness, and possibly fainting, especially when standing up)
Insomnia
Hallucinations (seeing, hearing, smelling, tasting or feeling things that are not there), amnesia and confusion
Twitching, twisting, or other unusual body movements
Unusual tiredness or weakness
Impulsive-compulsive behaviors: pramipexole (and related D3-preferring dopamine agonist medications such as ropinirole) can induce "impulsive-compulsive spectrum disorders" such as compulsive gambling, punding,  hypersexuality, and overeating, even in people without any prior history of these behaviours. Augmentation: Especially when used to treat restless legs syndrome, long-term pramipexole treatment may exhibit drug augmentation, which is "an iatrogenic worsening of RLS symptoms following treatment with dopaminergic agents" and may include an earlier onset of symptoms during the day or a generalized increase in symptoms.
Chronic administration of pramipexole may also result in desensitization of D3 autoreceptors, leading to reduced dopamine transporter function, "We show that prolonged administration of pramipexole (0.1mg/kg/day, 6 to 21 days) [equivalent to a low ~0.5 mg/day human dose], a preferential D3R agonist, leads to a decrease in DA [dopamine] uptake in mouse striatum that reflects a reduction in DAT [dopamine transporter] affinity for DA in the absence of any change in DAT density or subcellular distribution ... These observations provide novel insights into the long-term antiparkinson, antidepressant and additional clinical actions of pramipexole and other D3R agonists".As summarized in the following commentary, trials have shown mixed results, "Dopamine agonists, such as pramipexole—a relatively selective dopamine D3 receptor agonist—are thus potential treatments for depression, especially anhedonic depression. D3 receptors are found in the mesolimbic system, which in turn has been implicated in the motoric and hedonic deficits in depression ... The first randomized controlled trial in patients with non-treatment-resistant major depressive disorder, by Corrigan et al., evaluated three dosages of pramipexole. The lowest dosage (0.375 mg/day) did not differentiate from placebo. The efficacy of the highest dosage (5.0 mg/day) was not evaluable, because of a 58% attrition rate. The third dosage (1.0 mg/day) was more effective than placebo ... Cusin et al. compared adjunctive adjunctive pramipexole with placebo in an 8-week randomized double-blind trial with 60 outpatients with major depression for whom at least one adequate antidepressant medication trial (mean, two trials) had failed.