Well, not entirely. Not all the drugs used to treat sleep disorders are mimics of existing biomolecules. Some inhibit or modify the reception of the signaling molecules. This article talks about directly generating the substance itself.
The pills themselves also tend to be somewhat indiscriminate with where they cause the substance release. When you release a substance that does X into the body via the stomach, or even an injection, you end up with a lot more hitting receptor sites scattered across the body. For example, SSRIs often cause nausea since they affect the serotonin receptors in your GI tract. Just having serotonin released inside the brain would totally side-step this.
That said, my point is more about addiction. A large amount of sleeping pills are also common drugs of abuse, and can be highly addictive. A brain chip would not have nearly the same abuse potential.
The pills themselves also tend to be somewhat indiscriminate with where they cause the substance release. When you release a substance that does X into the body via the stomach, or even an injection, you end up with a lot more hitting receptor sites scattered across the body. For example, SSRIs often cause nausea since they affect the serotonin receptors in your GI tract. Just having serotonin released inside the brain would totally side-step this.
That said, my point is more about addiction. A large amount of sleeping pills are also common drugs of abuse, and can be highly addictive. A brain chip would not have nearly the same abuse potential.