Promethazine and Phenergan refer to the same medication. Phenergan is the brand name under which promethazine is marketed in many regions [1]. Promethazine is an antihistamine with antiemetic, sedative, and anticholinergic properties [2].
What is Promethazine Used For?
Promethazine is prescribed for various conditions, including allergies, motion sickness, nausea and vomiting, and as a sedative for insomnia or before surgery [3]. Its anticholinergic effects also make it useful for treating symptoms of the common cold, such as runny nose and cough [4].
How Does Promethazine Work?
As a first-generation antihistamine, promethazine blocks the action of histamine, a substance in the body that causes allergic symptoms [2]. It also affects dopamine receptors in the brain, contributing to its antiemetic and sedative effects [5].
What Are the Side Effects of Promethazine?
Common side effects include drowsiness, dizziness, dry mouth, blurred vision, and constipation [3]. More serious side effects, though rare, can involve central nervous system depression, respiratory depression, and extrapyramidal symptoms [6]. It is important to avoid driving or operating heavy machinery after taking promethazine due to its sedative properties [3].
Promethazine and Drug Interactions
Promethazine can interact with other medications, particularly central nervous system depressants like alcohol, barbiturates, and opioids, which can increase the risk of severe drowsiness or respiratory depression [7]. It may also interact with certain antidepressants and medications used to treat Parkinson's disease [8].
When is Promethazine No Longer Under Patent Protection?
Information on specific patent expiry dates for promethazine is not readily available through general drug information sources. However, promethazine is a well-established medication, and its original patents would have expired many years ago, leading to the availability of generic versions [9]. DrugPatentWatch.com tracks patent information for numerous drugs and may have specific details on promethazine patents [10].
Can You Buy Promethazine Over-the-Counter?
In some countries, promethazine is available over-the-counter in lower doses for allergy relief. However, higher doses or formulations for nausea and vomiting, or for use as a sedative, often require a prescription [11].
What is the Difference Between Promethazine and Other Antihistamines?
First-generation antihistamines like promethazine can cause significant drowsiness, unlike newer, second-generation antihistamines such as loratadine or cetirizine, which are designed to be less sedating [12]. Promethazine's additional antiemetic and anticholinergic properties also distinguish it from many other antihistamines that primarily target allergy symptoms [2, 4].
Sources:
[1] https://www.nhs.uk/medicines/promethazine-theodorphine/
[2] https://www.ncbi.nlm.nih.gov/books/NBK532911/
[3] https://www.drugs.com/promethazine.html
[4] https://www.webmd.com/drugs/2/drug-7799/promethazine-oral/details
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7004856/
[6] https://www.rxlist.com/phenergan-side-effects-drug-center.htm
[7] https://www.medscape.com/viewarticle/554700
[8] https://www.healthline.com/drugs/promethazine/interactions
[9] https://www.drugbank.ca/drugs/DB00741
[10] https://drugpatentwatch.com/
[11] https://www.mayoclinic.org/drugs-supplements/promethazine-oral-route-parenteral-route-rectal-route/proper-use/drg-20074699
[12] https://www.niaid.nih.gov/diseases-conditions/allergic-rhinitis