Medical Editor: John P. Cunha, DO, FACOEP Last updated on RxList: 9/7/2021
Tolak Side Effects Center

What Is Tolak?

Tolak (fluorouracil) Cream, 4%, is a nucleoside metabolic inhibitor indicated for the topical treatment of actinic keratosis lesions of the face, ears, and scalp.

What Are Side Effects of Tolak?

Common side effects of Tolak include application site reactions such as:

  • redness, scaling,
  • dryness,
  • crusting,
  • itching,
  • stinging,
  • burning,
  • swelling,
  • skin erosion,
  • sensitivity to sunlight, and
  • eye sensitivity reactions

Dosage for Tolak

Apply a dose of Tolak Cream once daily in an amount sufficient to cover the lesions of the face, ears, and/or scalp with a thin film, using the fingertips to gently massage the medication uniformly into the skin.

What Drugs, Substances, or Supplements Interact with Tolak?

Tolak may interact with systemic or topical steroids, immunosuppressants, immunomodulators, retinoids, glycolic acid products, alpha-hydroxy products, and chemical peeling products. Tell your doctor all medications, supplements, and skin treatments you use.

Tolak During Pregnancy and Breastfeeding

Tolak Cream is not recommended for use during pregnancy; it may harm a fetus. Consult your doctor before breastfeeding.

Additional Information

Our Tolak (fluorouracil) Cream, 4% 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.


Sun-Damaged Skin: Pictures of Sun Spots, Wrinkles, Sunburns See Slideshow
Tolak Consumer Information

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using fluorouracil topical and call your doctor at once if you have:

  • severe pain or swelling of treated skin;
  • severe itching, burning, or irritation;
  • new or worsening skin sores;
  • fever, chills; or
  • severe stomach pain, bloody diarrhea, vomiting.

Before your skin begins to heal it will become red, dry, tender, and crusty. This is a normal skin reaction, even if these symptoms get worse for a short time. Gradually, the dead skin will begin to shed off and you'll see raw skin appear. Ask your doctor when to stop using the medicine after you notice signs of healing.

Common side effects may include:

  • skin pain, itching, burning, or irritation;
  • skin darkening or scarring;
  • skin redness and swelling; or
  • small blood vessels under the skin.

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.

Read the entire detailed patient monograph for Tolak (Fluorouracil Cream, 4%)


Self-examination is important in the detection of skin cancer. See Answer
Tolak Professional Information


The following serious adverse reactions are discussed in more detail in other sections of the labeling:

  • Application Site Adverse Reactions [see WARNINGS AND PRECAUTIONS]
  • Hypersensitivity Reactions [see WARNINGS AND PRECAUTIONS]
  • Ophthalmic Adverse Reactions [see WARNINGS AND PRECAUTIONS]
  • Photosensitivity [see WARNINGS AND PRECAUTIONS]
  • Embryofetal toxicity [see WARNINGS AND PRECAUTIONS]
  • Toxicity in Patients with Dihydropyrimidine Dehydrogenase Deficiency [see WARNINGS AND PRECAUTIONS]

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The data described below reflect exposure to Tolak Cream in 397 subjects with actinic keratosis in vehicle-controlled trials. The population ranged in age from 33 to 94 years, was 80% male, and almost all were Caucasian. Most subjects were treated with Tolak Cream once daily for 4 weeks. Throughout the 4-week treatment and the 4-week post-treatment periods, the trials specifically monitored for adverse reactions related to tolerability, including erythema, scaling/dryness, edema, crusting, erosions, stinging/burning, and pruritus.

The number and percentage of subjects with each of these monitored adverse reactions at one or more post-baseline visit(s) during the clinical trials are shown in Table 1.

Table 1: Incidence of Application Site Adverse Reactions Occurring with 4 Weeks of Tolak Cream Treatment in Clinical Trials 1 and 2

Tolak Cream
N=397 n (%)
N=120 n (%)
Mild, Moderate or SevereSevere OnlyMild, Moderate or SevereSevere Only
Erythema394 (99%)174 (44%)102 (85%)0 (0%)
Scaling/ Dryness377 (95%)94 (24%)99 (83%)0 (0%)
Crusting346 (87%)87 (22%)46 (38%)0 (0%)
Pruritus337 (85%)65 (16%)46 (38%)1 (1%)
Stinging/ Burning346 (87%)101 (25%)42 (35%)0 (0%)
Edema275 (69%)30 (8%)11 (9%)0 (0%)
Erosions271 (68%)44 (11%)14 (12%)0 (0%)

In these clinical trials, the intensity of the adverse reactions in subjects using Tolak Cream generally increased over the 4-week treatment period, usually reaching maximal levels at 4 weeks of treatment and then diminishing to baseline levels within 4 weeks after cessation of treatment.

In Trials 1 and 2, 11% of Tolak Cream-treated and 3% of vehicle-treated subjects discontinued treatment because of adverse reactions. Of these subjects, the majority had adverse reactions at the application site. Eye swelling, leading to discontinuation, occurred in one subject with Tolak Cream use.

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of topical fluorouracil. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Blood and Lymphatic System Disorders : leukocytosis, pancytopenia, thrombocytopenia, eosinophilia, neutrophil toxic granulation

Eyedisorders : corneal disorder, conjunctival disorder, eye irritation, conjunctivitis, lacrimation

Gastrointestinal disorders : stomatitis

General Disorders and Administration Site Conditions :medicinal taste

Infections and Infestations : herpes simplex

Neoplasms : chronic lymphocytic leukemia, non-melanoma skin cancer

Nervous system disorders : insomnia, irritability

Psychiatric disorders : emotional distress

Skin and subcutaneous tissue disorders : blistering, allergic contact dermatitis, photosensitivity, pain, scarring, skin irritation, rash, ulceration, hyperpigmentation, alopecia, bullous pemphigoid, ichthyosis, suppuration, swelling, soreness, telangiectasia, tenderness, urticaria

Read the entire FDA prescribing information for Tolak (Fluorouracil Cream, 4%)

© Tolak Patient Information is supplied by Cerner Multum, Inc. and Tolak Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

Health Solutions From Our Sponsors