Dichloralphenazone is one of three ingredients in the headache drug, Midrin. The other two ingredients are isometheptene, a drug that constricts blood vessels and acetaminophen. Midrin actually is a combination of four drugs because dichloralphenazone is broken down in the body into chloral hydrate, which is an old sedative hypnotic drug used for insomnia and antipyrine, a non-steroidal anti-inflammatory pain medicine.

Midrin is a very old drug which was introduced before the 1962 Congressional act that required rigorous clinical trials for the FDA approval. It has been marketed for both migraine and tension-type headaches.

Because Midrin contains a sedative medications, which is potentially addictive, it is considered to be a controlled drug. The supply of Midrin has been very inconsistent because it lacks an official FDA approval and because very few doctors prescribe it. When it is not available from a pharmaceutical manufacturer some doctors order it from a compounding pharmacy, which makes Midrin by mixing the three individual ingredients by hand in small batches.

Midrin (acetaminophen, isometheptene and dichloralphenazone)

Side Effects:
RxList
rxlist.com Midrin Information: https://www.rxlist.com/midrin-drug.htm
Dizziness, drowsiness, or nausea may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Breastfeeding:

Summary of Use During Lactation:

Short-term or occasional use of dichloralphenazone during breastfeeding is unlikely to adversely affect the breastfed infant, especially if the infant is older than 2 months.

Because the active metabolite, trichloroethanol, has a long half-life, long-term use of repeated doses during breastfeeding could result in infant sedation, especially while nursing a neonate or preterm infant. The low doses of dichloralphenazone found in combination migraine products (e.g., Midrin) are less likely to cause drowsiness in the infant unless doses are repeated several times daily. The antipyrine component of dichloralphenazone is considered unlikely to harm the infant.

Monitor the infant for excessive drowsiness during use.

Drug Levels:
Dichloralphenazone is a chemical combination of chloral hydrate (64%) and antipyrine (36%).

Dichloralphenazone Drug Levels and Effects:
https://www.ncbi.nlm.nih.gov/books/NBK501312/

A mild Sedative