Tetracyclics are chemical compounds that contain four interconnected rings of atoms, e.g. Tröger's base.
![](http://wikiimg.tojsiabtv.com/wikipedia/commons/thumb/4/40/Doxycycline_structure.svg/200px-Doxycycline_structure.svg.png)
Doxycycline, a tetracyclic antibiotic.
![](http://wikiimg.tojsiabtv.com/wikipedia/commons/thumb/9/94/Mirtazapine.svg/200px-Mirtazapine.svg.png)
Mirtazapine, a tetracyclic antidepressant.
They have various pharmaceutical uses, for instance the tetracycline antibiotics and the tetracyclic antidepressants.