Is doxycycline safe for long term use for acne?

Usually safe. : It is generally well tolerated. Incidence of adverse effects for doxycycline is around 2.3 patients per million patients per year. Esophageal erosions and photosensitivity are the most common, but usually rare. Source: Clin Cosmet Investig Dermatol. 2009;2:129-140.

Dr Hegab agreed

Yes: Doxycycline is used for severe acne. It often needs to be taken for 6-8 weeks before results are seen, and some patients take it indefinitely / long-term to prevent scarring from occurring related to inflammation or infection. One common side effect is sensitivity to the sun and easy burning and may require wearing sunscreen. However, that doesn’t necessarily make the drug less “safe”.