Medical Editor: John P. Cunha, DO, FACOEP Last updated on RxList: 5/31/2023

Drug Summary

What Is Hydro-Q?

Hydro-Q (hydroquinone gel) is a depigmenting agent indicated for the gradual bleaching of hyperpigmented skin conditions such as chlosma, melasma, freckles, senile lentigines and areas of melanin hyperpigmentation.

What Are Side Effects of Hydro-Q?

Side effects of Hydro-Q include:

Seek medical care or call 911 at once if you have the following serious side effects:

  • Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
  • Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheadedness, or passing out;
  • Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors.

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

Dosage for Hydro-Q

A dose of Hydro-Q is applied to the affected areas twice daily, morning and before bedtime or as directed by a physician.

Hydro-Q In Children

Safety and effectiveness of Hydro-Q in pediatric patients below the age of 12 years have not been established.

What Drugs, Substances, or Supplements Interact with Hydro-Q?

Hydro-Q may interact with other medicines.

Tell your doctor all medications and supplements you use.

Hydro-Q During Pregnancy and Breastfeeding

Tell your doctor if you are pregnant or plan to become pregnant before using Hydro-Q; it is unknown how it would affect a fetus. It is unknown if Hydro-Q passes into breast milk. Consult your doctor before breastfeeding.

Additional Information

Our Hydro-Q (hydroquinone gel) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Drug Description
ins hydroquinone USP 4%. Hydroquinone is 1, 4-Benzenediol {CAS 123-31-91}. Hydroquinone is structurally related to monobenzone. Hydroquinone occurs as fine white needles. The drug is freely soluble in water and in alcohol and has a pKa of 9.96.

Chemically, hydroquinone is designated as p-dihydroxybenzene; the empirical formula is C6H6O2; The molecular weight is 110.1. The structural formula is:

Figure A

Hydro-q (hydroquinone) Structural Formula Illustration

Active Ingredient

Hydroquinone USP 4%

Other Ingredients

Purified water, Carbomer 940, Sodium Metabisulfite, Sodium Hydroxide, Methylparaben, Edetate Disodium.

Indications & Dosage


HYDRO-Q is indicated for the gradual bleaching of hyperpigmented skin conditions such as chlosma, melasma, freckles, senile lentigines and areas of melanin hyperpigmentation.


HYDRO-Q should be applied to the affected areas twice daily, morning and before bedtime or as directed by a physician.

During and after the use of HYDRO-Q , sun exposure should be limited and a sunscreen agent or protective clothing should be used to cover up the treated areas to prevent regimentation. If no lightening effect is noted after two months of treatment, use of HYDRO-Q should be discontinued. There is no recommended dosage for children under the age of 12 years of age except under the advice and supervision of a


Dosage Forms And Strengths

HYDRO-Q (Hydroquinone 4%) Gel is supplied in a 30 g tube.

NDC: 30815-0040-1

Store at controlled room temperature, between 15° and 30°C (59°and 86°F).


1. Denton C, Fitzpatrick TB, Lerner AB. Inhibition of melanin formation by chemical agents. J Invest Dermatology. 1952; 18: 119-135.
2. Fitzpatrick TB, Jimbow K, Obata M, Panthak M. Mechanism of depigmentation by hydroquinone. J Invest Dermatology. 1974; 62: 436-
3. Anderson RR, Parrish JA, Pitts D, Urbach F. UVA, Biological Effects of Ultraviolet Radiation With Emphasis on Human Responses to Longwave Ultraviolet. New York and London: Plenum Press; 1978: 151.

Distributed by: DermAvance Pharmaceuticals, Malvern, PA 19355. Revised: Nov 2019

Side Effects & Drug Interactions


No systemic reactions have been reported. Occasional cutaneous hypersensitivity (localized contact dermatitis) may occur, in which case the medication should be discontinued and the physician notified immediately


No information provided.

Warnings & Precautions


  1. CAUTION: Hydroquinone is a depigmenting agent that may produce unwanted cosmetic effects if not used as directed. The physician should be familiar with the contents of this insert before prescribing or dispensing this medication.
  2. Test for skin sensitivity before using HYDRO-Q by applying a small amount of the gel to an unbroken patch of skin and check within 24 hours. Minor redness is not a contraindication but where there is itching and vesicle formation or excessive inflammatory response further treatment is not advised. Close patient supervision is recommended. Contact with the eyes should be avoided. If no lightening effect is noted after 2 months of treatment the use of HYDRO-Q should be discontinued. HYDRO-Q is formulated for the treatment of dyschromia and should not be used for the prevention of sunburn.
  3. Sunscreen use is an essential aspect of hydroquinone therapy because even minimal sunlight sustains melanocytic activity. To prevent repigmentation during treatment and maintenance therapy, sun exposure on treated skin should be avoided by application of a broad spectrum sunscreen SPF 15 or greater) or by use of protective clothing D. Keep this and all medications out of reach of children. In case of accidental ingestion, contact a physician or a poison control center immediately.
  4. WARNING: Contains sodium metabisulfite, a sulfite that may cause serious allergic reactions (e.g., hives, itching, wheezing, anaphylaxis, severe asthma attack) in certain susceptible persons
  5. On rare occasions, a gradual blue-black darkening of the skin may occur, in which case, use of HYDRO-Q should be discontinued and a physician contacted immediately



Pregnancy Category C

Animal reproduction studies have not been conducted with topical hydroquinone. It is also not known whether hydroquinone can cause fetal harm when used topically on a pregnant woman, or can affect reproductive capacity.

Nursing mothers

It is not known whether topical hydroquinone is absorbed or excreted in human milk. Caution is advised when used by a nursing mother.

Pediatric Usage

Safety and effectiveness in pediatric patients below the age of 12 years have not been established.

Overdose & Contraindications


There have been no systemic reactions reported from the use of topical hydroquinone. However, treatment should be limited to relatively small areas of the body at one time, since some patients experience a skin reddening and a mild burning sensation that does not preclude treatment


HYDRO-Q is contraindicated in any patient that has a prior history of sensitivity or allergic reaction to hydroquinone or any of the other ingredients. The safety of topical hydroquinone use during pregnancy or in children (12 years and under) has not been established.

Clinical Pharmacology


Topical application of hydroquinone produces a reversible depigmentation of the skin by inhibition of the enzymatic hydroquinone. oxidation of tyrosine to 3, 4-dihydroxyphenylalanine (dopa) 1 and suppression of other melanocyte metabolic processes. Exposure to sunlight or ultraviolet light will cause regimentation of the bleached areas.

Medication Guide


No information provided. Please refer to the WARNINGS AND PRECAUTIONS section.

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