When drugs appear in a dream – whether self-administered or not – this suggests that we may need external help to enable us to change our inner perceptions.
To be taking drugs suggests we feel we have relinquished control of a situation in our waking lives and are having to rely on external stimuli.
To have an adverse drug reaction in dreams could mean that we fear madness.
To be given drugs against our will indicates that we are being forced to accept an unpalatable truth. You might like to consult the entries for alcohol / alcoholic, drunk and medication / medicine.