2026 data ClinicalTrials.gov official source

Conditions: O

Compiled by PlainTrial Editorial, Clinical Trial Intelligence Editorial Team · January 1, 2026

Every condition beginning with O that has a registered US clinical trial, with how many studies cover each.

829 conditions starting with "O"

Showing 301–350 of 829

Condition	Trials	Recruiting
Opioid Consumption, Postoperative	2	2
Opioid Court Model	1	-
Opioid Craving	3	2
Opioid Dependence	30	8
Opioid Dependence With Current Use (Disorder)	1	1
Opioid Dependency	3	1
Opioid Medication Assisted Treatment	2	1
Opioid Misuse	14	4
Opioid Misuse and Addiction	1	1
Opioid Overdose	9	6
Opioid Overdose Prevention	1	1
Opioid Prescribing	3	-
Opioid Safety	1	-
Opioid Stewardship	1	-
Opioid Substitution Treatment	1	1
Opioid Substitution Treatment Clinics	1	-
Opioid Tolerance	1	-
Opioid Use	106	46
Opioid Use Disorder	258	156
Opioid Use Disorder (OUD)	8	5
Opioid Use Disorder, Moderate	2	1
Opioid Use Disorder, Severe	2	1
Opioid Use Disorders	3	1
Opioid Use, Unspecified	10	2
Opioid Use, Unspecified, Uncomplicated	1	-
Opioid Withdrawal	10	4
Opioid Withdrawal (Disorder)	1	-
Opioid-induced Constipation	6	1
Opioid-Induced Esophageal Dysfunction	1	1
Opioid-Induced Hyperalgesia	1	-
Opioid-Related Disorders	59	8
Opioid-Related Severe Adverse Drug Event	1	-
Opioid; Intoxication, Perception Disturbance (Acute)	1	-
Opioids	1	1
Opioids; Harmful Use	3	-
Opiophobia	1	-
Opportunistic Infections	1	1
Oppositional Defiant Disorder	8	3
Opsoclonus-myoclonus Syndrome	1	-
Optic Atrophy	2	1
Optic Disc Edema	1	1
Optic Glioma	2	-
Optic Nerve Atrophy	2	1
Optic Nerve Disease	1	1
Optic Nerve Diseases	3	2
Optic Nerve Glioma	1	-
Optic Nerve Head Pits, Bilateral Congenital	1	1
Optic Nerve Hypoplasia	1	1
Optic Nerve Hypoplasia and Abnormalities of the Central Nervous System	1	1
Optic Neuritis	6	3

Data sourced from official public datasets. See our methodology for details.