With careful use of antihistamines central effects may be minimised or even largely avoided while adequate peripheral antihistaminic activity is preserved. Tolerance to central effects may develop quickly with some drugs, so that sedation is no longer troublesome after a few days. With sustained-release antihistamines, early-evening dosage may provide sufficient activity, without sedation, the next day. For patients in whom daytime sedation is troublesome three drugs, astemizole, mequitazine, and terfenadine, are likely to prove useful. However, the response of the individual patient cannot be predicted, and the possibility of sedation can never be completely excluded.