Editing Somnolence (section)

== Causes ==
[[File:Biological clock human.svg|thumb|340px|Some features of the human circadian (24-hour) biological clock. ''Click to enlarge'']]

=== Circadian rhythm disorders ===
{{Main|Circadian rhythm sleep disorder}}
Circadian rhythm ("biological clock") disorders are a common cause of drowsiness as are a number of other conditions such as sleep apnea, insomnia and narcolepsy.<ref name=":0"/> The body clock disorders are classified as extrinsic (externally caused) or intrinsic. The former type is, for example, shift work sleep disorder, which affects people who work nights or rotating shifts. The intrinsic types include:<ref>{{Cite web|title = Circadian Sleep Disorders Network|url = http://www.circadiansleepdisorders.org/|website = www.circadiansleepdisorders.org|access-date = 2015-11-02}}</ref>
* [[Advanced sleep phase disorder]] (ASPD) – A condition in which patients feel very sleepy and go to bed early in the evening and wake up very early in the morning
* [[Delayed sleep phase disorder]] (DSPD) – Faulty timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily cycles such that they occur a number of hours late compared to the norm, often misdiagnosed as insomnia
* [[Non-24-hour sleep–wake disorder]] – A faulty body clock and sleep-wake cycle that usually is longer than (rarely shorter than) the normal 24-hour period causing complaints of insomnia and excessive sleepiness
* [[Irregular sleep–wake rhythm]] – Numerous naps throughout the 24-hour period, no main nighttime sleep episode and irregularity from day to day

=== Physical illness ===
Sleepiness can also be a response to infection.<ref>{{cite journal |first1=Janet |last1=Mullington |first2=Carsten |last2=Korth |first3=Dirk M. |last3=Hermann |first4=Armin |last4=Orth |first5=Chris |last5=Galanos |first6=Florian |last6=Holsboer |first7=Thomas |last7=Pollmächer |title=Dose-dependent effects of endotoxin on human sleep |journal=American Journal of Physiology. Regulatory, Integrative and Comparative Physiology |volume=278 |issue=4 |pages=R947–55 |year=2000 |pmid=10749783 |doi=10.1152/ajpregu.2000.278.4.r947|s2cid=10272455 }}</ref> Such somnolence is one of several [[sickness behavior]]s or reactions to infection that some theorize evolved to promote recovery by conserving energy while the body fights the infection using fever and other means.<ref name="Hart">{{cite journal |doi=10.1016/S0149-7634(88)80004-6|title=Biological basis of the behavior of sick animals|journal=Neuroscience & Biobehavioral Reviews|volume=12|issue=2|pages=123–37|year=1988|last1=Hart|first1=Benjamin L.|pmid=3050629|s2cid=17797005}}</ref><ref>{{cite journal |doi=10.1016/S0889-1591(02)00077-6|title=Cytokine-induced sickness behavior|journal=Brain, Behavior, and Immunity|volume=17|pages=112–118|year=2003|last1=Kelley|first1=Keith W.|last2=Bluthé|first2=Rose-Marie|last3=Dantzer|first3=Robert|last4=Zhou|first4=Jian-Hua|last5=Shen|first5=Wen-Hong|last6=Johnson|first6=Rodney W.|last7=Broussard|first7=Suzanne R.|pmid=12615196|issue=1|s2cid=25400611}}</ref> Other causes include:<ref>{{Cite web|title = Drowsiness: MedlinePlus Medical Encyclopedia|url = https://www.nlm.nih.gov/medlineplus/ency/article/003208.htm|website = www.nlm.nih.gov|access-date = 2015-10-31}}</ref>
* [[Anxiety]] 
* [[Brain tumor]]
* [[Chronic pain]]s
* [[Concussion]] – a mild traumatic brain injury 
* [[Diabetes]]
* [[Fibromyalgia]]
* [[Head injury]]
* [[Hypercalcemia]] – too much calcium in the blood
* [[Hypermagnesemia]]
* [[Hyponatremia]] – low blood sodium 
* [[Hypothyroidism]] – the body doesn't produce enough hormones that control how cells use energy
* [[Meningitis]]
* [[Mood disorder]]s – [[Depression (mood)|depression]]
* [[Multiple sclerosis]] 
* [[Narcolepsy]] – disorder of the nervous system
* [[Skull fracture]]s
* [[African trypanosomiasis|Sleeping sickness]] – caused by a specific parasite
* [[Stress (biology)|Stress]]

=== Medicine ===
{{more citations needed|section|date=November 2019}}

* [[Analgesic]]s – mostly prescribed or illicit [[opiate]]s such as [[OxyContin]] or [[heroin]]
* Anticonvulsants / [[antiepileptic]]s – such as [[phenytoin]] (Dilantin), [[carbamazepine]] (Tegretol), [[Pregabalin]] (Lyrica) and [[Gabapentin]] (Neurontin)
* [[Antidepressants]] – for instance, sedating [[tricyclic antidepressants]]<ref name="pmid16832696">{{cite journal |last1=Zimmermann |first1=C. |last2=Pfeiffer |first2=H. |title=Schlafstörungen bei Depression: Behandlungsmöglichkeiten |journal=Der Nervenarzt |date=January 2007 |volume=78 |issue=1 |pages=21–30 |doi=10.1007/s00115-006-2111-1 |pmid=16832696 |trans-title=Sleep Disorders in Depression: Treatment options |language=German}}</ref> [[amitriptyline]] and  [[mirtazapine]]. Somnolence is less common with [[SSRI]]s<ref name="pmid22161405">{{cite journal |last1=Watanabe |first1=Norio |last2=Omori |first2=Ichiro M |last3=Nakagawa |first3=Atsuo |last4=Cipriani |first4=Andrea |last5=Barbui |first5=Corrado |last6=Churchill |first6=Rachel |last7=Furukawa |first7=Toshi A |year=2011 |title=Mirtazapine versus other antidepressive agents for depression |journal=Cochrane Database of Systematic Reviews |issue=12 |pages=CD006528 |pmid=22161405 |pmc=4158430 |doi=10.1002/14651858.CD006528.pub2}}</ref> and [[SNRI]]s as well as [[MAOI]]s.
* [[Antihistamines]] – for instance, [[diphenhydramine]] ([[Benadryl]], [[Nytol]]), [[doxylamine]] (Unisom-2), [[hydroxyzine]] (Atarax) and [[promethazine]] (Phenergan)
* [[Antipsychotics]] – for example, [[Lurasidone]] (Latuda), [[thioridazine]], [[quetiapine]] (Seroquel), [[olanzapine]] (Zyprexa), [[risperidone]] and [[ziprasidone]] ([[Geodon]]) but not [[haloperidol]]
* [[Dopamine agonists]] used in the treatment of [[Parkinson's disease]] – e.g. [[pergolide]], ropinirole and [[pramipexole]].
* [[HIV]] medications – such as [[efavirenz]]
* [[Hypertension]] medications – such as [[amlodipine]]
* [[Hypnotic]]s, or soporific drugs, commonly known as sleeping pills.
* [[Tranquilizers]] – such as [[zopiclone]] (Zimovane), or the [[benzodiazepine]]s such as [[diazepam]] (Valium) or [[nitrazepam]] (Mogadon) and the [[barbiturate]]s, such as [[amobarbital]] (Amytal) or [[secobarbital]] (Seconal)
* Other agents impacting the [[central nervous system]] in sufficient or toxic doses