Caffeine is an adenosine antagonist. Here they are side by side for comparison.
<a href="//commons.wikimedia.org/wiki/User:%D0%94.%D0%98%D0%BB%D1%8C%D0%B8%D0%BD" title="User:Д.Ильин">Д.Ильин</a>: translation
<ul><li>derivative work: — <b><a href="//commons.wikimedia.org/wiki/User:Delhovlyn" title="User:Delhovlyn">Delhovlyn</a></b> <small>(<a href="//commons.wikimedia.org/wiki/User_talk:Delhovlyn" title="User talk:Delhovlyn">discuter / talk</a>)</small></li>
<li><a href="//commons.wikimedia.org/wiki/File:Caffeine_and_adenosine.svg" title="File:Caffeine and adenosine.svg">Caffeine_and_adenosine.svg</a>: Icey</li></ul>