An antitussive having high activity, which is free from side effects such as psychotomimetic, which may also be administered orally is disclosed. The antitussive according to the present invention comprises as an effective ingredient a .delta.-opioid antagonist or a pharamaceutically acceptable salt thereof.

TECHNICAL FIELD 
The present invention relates to an antitussive. 
BACKGROUND ART 
Conventional antitussives are provided by mixing drugs which variously 
affect central nervous system, such as codeine and dextromethorphan. 
However, these drugs have serious side effects such as drug dependence and 
psychotomimetic, so that close attention should be paid when using these 
antitussives. 
In recent years, antitissive effect of .mu. and .kappa. agonists of opioid 
is drawing attention. However, conventional agonists such as morphine and 
codeine have problems that they cause drug dependence and conventional 
.kappa.-agonists have problems that they cause aversion and 
psychotomimetic. Under these circumstances, an excellent antitussive free 
from psychotomimetic, drug dependence and aversion is demanded. 
DISCLOSURE OF THE INVENTION 
An object of the present invention is to provide a novel antitussive having 
high activity, of which action mechanism is different from that of the 
above-mentioned conventional antitussives having serious side effects such 
as drug dependence, psychotomimetic and aversion, which is free from the 
side effects that the conventional antitussives have, and which may also 
be used as an oral drug. 
The present inventors intensively studied to develop the above-mentioned 
ideal antitussive to discover that antagonists of .delta. opioid receptor 
have strong antitussive effect, which have an action mechanism totally 
different from that of the conventional morphine, codeine and 
dextromethorphan, thereby completing the present invention. Unlike the 
agonists of opioid, the .delta.-antagonists do not cause drug dependence, 
psychotomimetic and aversion, so that selective antitussive effect can be 
expected. 
That is, the present invention provides an antitussive comprising as an 
effective ingredient a .delta.-opioid antagonist or a pharmaceutically 
acceptable salt thereof. 
By the present invention, an antitussive of which action mechanism is 
totally different from that of the conventional antitussives having 
serious side effects such as drug dependence, psychotomimetic and 
aversion, which has a high activity and which may also be orally 
administered was provided.