Tretinoin, also known as all-trans retinoic acid (ATRA), is a medication used for the treatment of acne and acute promyelocytic leukemia. For acne, it is applied to the skin as a cream, gel or ointment. For acute promyelocytic leukemia, it is effective only when the RARA-PML fusion mutation is present and is taken by mouth for up to three months. Topical tretinoin is also the most extensively investigated retinoid therapy for photoaging.

Common side effects when used as a cream are limited to the skin and include skin redness, peeling, and sun sensitivity. When taken by mouth, side effects include hypertriglyceridemia, hypercholesterolemia, shortness of breath, headache, numbness, depression, skin dryness, itchiness, hair loss, vomiting, muscle pains, and vision changes. Other severe side effects include high white blood cell counts and blood clots. Use during pregnancy is contraindicated due to the risk of birth defects. It is in the retinoid family of medications.

Tretinoin was patented in 1957 and approved for medical use in 1962. It is on the World Health Organization's List of Essential Medicines. Tretinoin is available as a generic medication. In 2023, it was the 197th most commonly prescribed medication in the United States, with more than 2 million prescriptions.

Tretinoin is most commonly used to treat acne, both inflammatory and noninflammatory. Multiple studies support the efficacy of topical retinoids in the treatment of acne vulgaris. It is sometimes used in conjunction with other topical acne medications to enhance their penetration. In addition to treating active acne, retinoids accelerate the resolution of acne-induced postinflammatory hyperpigmentation. It is also useful as maintenance therapy for people who have responded well to their initial treatment, reducing the prolonged use of antibiotics for acne.

Photoaging is premature skin aging resulting from prolonged and repeated exposure to solar radiation. Features of photoaging include fine and coarse wrinkles, changes in skin pigmentation, and loss of elasticity. In human skin, topical retinoids increase collagen production, induce epidermal hyperplasia, and decrease keratinocyte and melanocyte atypia. Topical tretinoin is the most extensively investigated retinoid therapy for photoaging. Topical tretinoin can be used for mild to severe photoaging in people of all skin types. Several weeks or months of use are typically required before improvement is appreciated. Although it has only been studied for up to two years, it may be continued indefinitely. A long-term maintenance regimen with a lower concentration or less frequent application may be an alternative to continued use.

Topical tretinoin is available in several formulations, including creams, gels, microsphere gels, and lotions.

The chemical stability of tretinoin is significantly affected by light and oxidizing agents. When combined with 10% benzoyl peroxide and exposed to light, significant degradation occurs, with over 50% of the compound degrading within approximately two hours and up to 95% within 24 hours.

To address this instability, alternative formulations have been developed. The microsphere gel formulation utilizes microsponge technology, encapsulating tretinoin within an aqueous gel matrix to enhance stability and control the release of the active ingredient. When microencapsulated tretinoin is exposed to benzoyl peroxide and light, it exhibits improved stability, with only approximately 1% degradation after four hours and approximately 13% after 24 hours.