Which of the following is *not* considered a controlled substance?

Ergotamine Tartrate is not classified as a controlled substance under the Controlled Substances Act. This medication is primarily used to treat migraine headaches due to its vasoconstrictive properties and does not possess a high potential for abuse or dependence compared to the other substances listed.

In contrast, Secobarbital, a barbiturate, is a central nervous system depressant that can lead to dependence and has a significant potential for abuse, thus classified as a Schedule II controlled substance. Morphine, a potent opioid analgesic, is also a Schedule II controlled substance due to its high potential for addiction and misuse. Additionally, Papaverine, while not as commonly recognized as a controlled substance, is considered a Schedule IV drug in some jurisdictions due to its use related to vascular conditions and potential for misuse. Hence, Ergotamine Tartrate stands out as not being under controlled substance regulations.