Overview

For a patient with PD, a drug may act in several ways: by a non-specific beneficial effect on a range of PD features, by a relatively specific effect, or by targeting a co-occurring psychiatric disorder. Also, a placebo effect can be marked.

Drugs are prescribed for many patients with PDs, although their effects are often unpredictable. The most commonly prescribed classes are neuroleptics and antidepressants, while lithium carbonate, anticonvulsants, anxiolytics and psychostimulants have also been used. But an individual patient may benefit from each of several drugs, while an individual drug may have effects on a range of target symptoms and behaviours. Also, there can be a considerable variability of response to a drug regime within a group of patients selected on the basis of PD.

Some of the many factors that account for such variability include an inconsistent placebo response and the heterogeneity of a patient sample in relation to PD features and to co-occurring psychiatric disorders, particularly co-occurring depressive disorders.

Investigations of drug treatments for PD are complicated by methodological problems in the assessment of PDs and by the need to assess a range of outcome measures. Compliance with treatment is often poor and the effects of some drugs may take time to develop, for example several weeks in relation to the effects of neuroleptics on some features of borderline PD. Also, self-reports of change do not always correspond with clinicians' ratings.